ziad said - Academia.edu (original) (raw)

Papers by ziad said

Research paper thumbnail of Assessing the Science Interest, Attitude, and Self-Efficacy of Qatari Students at the Preparatory, Secondary, and University Levels

Eurasia Journal of Mathematics, Science and Technology Education

A large sample (n = 1,799) of Qatari female and male students at the preparatory, secondary, and ... more A large sample (n = 1,799) of Qatari female and male students at the preparatory, secondary, and university levels responded to Likert items about their interest, attitude, and self-efficacy regarding science. The items were similar to those of TIMSS and PISA, but improved upon them in several ways. The findings suggest that Qatari students are positive in their interest, attitude, and self-efficacy, but not as positive as TIMSS and PISA report. The findings raise an important question: If the students' interest, attitude, and self-efficacy are positive, then why do the students have relatively low achievement scores on TIMSS and PISA? The answer may be the instructional methods and conditions of a developing educational system. The present findings have implications for all countries that use TIMSS and PISA, particularly those countries with developing educational systems, rapidly expanding economies, and an increasing need for students in science careers.

Research paper thumbnail of Teaching Style Differences between Male and Female Science Teachers in Qatari Schools: Possible Impact on Student Achievement

Eurasia Journal of Mathematics, Science and Technology Education

In Qatar's gender-segregated public schools, female students outperform male students in internat... more In Qatar's gender-segregated public schools, female students outperform male students in international science tests such as PISA and TIMMS. In contrast to the international trend for top performing countries, however, female students report lower levels of interest in science-based careers than males. One possible factor that may contribute to this discrepancy is the difference in teaching styles between female teachers and their male counterparts. In this paper we focus on results obtained from 105 classroom observations (39 males and 66 females) selected from 50 different public schools as part of two independent research projects to study the motivation factors and attitudes toward and interest in science among Qatari students. In addition, 40 semi-structured interviews of students, teachers and administrators were conducted. The observations were guided using an adopted Reformed Teaching Observation Protocol (RTOP) evaluation rubric consisting of 13 teaching traits which provides a standardized mean for detecting the degree to which science classroom instruction is reformed through a focus on Lesson Design, Content, Pedagogic Knowledge and classroom culture. Female teachers provided better delivery during theory classes, whereas male teachers demonstrated better performance in laboratory-based classes.

Research paper thumbnail of Comparing Likert Scale Functionality Across Culturally and Linguistically Diverse Groups in Science Education Research: an Illustration Using Qatari Students’ Responses to an Attitude Toward Science Survey

International Journal of Science and Mathematics Education

Surveying is a common methodology in science education research, including cross-national and cro... more Surveying is a common methodology in science education research, including cross-national and cross-cultural comparisons. The literature surrounding students' attitudes toward science, in particular, illustrates the prevalence of efforts to translate instruments with the eventual goal of comparing groups. This paper utilizes survey data from a nationally representative crosssectional study of Qatari students in grades 3 through 12 to frame a discussion around the adequacy and extent to which common adaptations allow comparisons to be made among linguistically or culturally different respondents. The analytic sample contained 2,615 students who responded to a previously validated 32-item instrument, 1,704 of whom completed the survey in Modern Standard Arabic and 911 in English. The purpose of using these data is to scrutinize variation in the performance of the instrument between groups of respondents as determined by language of survey completion and cultural heritage. Multi-group confirmatory factor analysis was employed to investigate issues of validity associated with the performance of the survey with each group, and to evaluate the appropriateness of using this instrument to make simultaneous comparisons across the distinct groups. Findings underscore the limitations of group comparability that may persist even when issues of translation and adaptation were heavily attended to during instrument development.

Research paper thumbnail of Science Education Reform in Qatar: Progress and Challenges

EURASIA Journal of Mathematics, Science & Technology Education

Science education reform in Qatar has had limited success. In the Trends in International Mathema... more Science education reform in Qatar has had limited success. In the Trends in International Mathematics and Science Study (TIMMS), Qatari 4th and 8th grade students have shown progress in science achievement, but they remain significantly below the international average. Also, in the Program for International Student Assessment (PISA), Qatari students have shown progress in science achievement, but they are again below the international average. To gain insight into what factors limit the students' science achievement, the School Science Teaching Inventory Questionnaire (SSTIQ) was administered to science coordinators and teachers in 24 independent schools in Qatar. The questionnaire results, in conjunction with interviews, indicated that science coordinators and teachers believed that a set of factors was responsible, and that low student motivation was the factor that was most responsible. Low student motivation was due, in part, to textbooks being overemphasized, and inquiry-based and problem-based methods being underemphasized. Based on these findings, recommendations for improving students' science achievement were provided.

Research paper thumbnail of The Impact of Long Teachers’ Training on Performance and Attitude Toward Science of Both Teachers and Students-The Case of Secondary School Teachers

INTED2017 Proceedings, 2017

Research paper thumbnail of Attitudes toward science among grades 3 through 12 Arab students in Qatar: findings from a cross-sectional national study

International Journal of Science Education, 2016

Research paper thumbnail of ‘Qatari Students’ Interest in Attitudes toward Science: the Impact of the Educational Reform on Science Education in Qatar

Qatar Foundation Annual Research Forum Proceedings, Dec 14, 2011

Research paper thumbnail of Qatari Students Performance, Interest In, and Attitude Towards Science and Mathematics

Despite the resources that have been invested in the educational reform in Qatar in the last few ... more Despite the resources that have been invested in the educational reform in Qatar in the last few years, no systematic study has been conducted to investigate the factors behind the disengagement and disinterest in science and mathematics in Qatari schools. This paper explores why the Qatari education reforms launched in 2003 as “Education for a New Era” have not reversed the significant decline observed over the past 15 years in the number of students studying mathematics and science at both secondary and tertiary levels of education although a significant relative progress has been observed in the recently published international results of TIMMS 2011 as compared to previous TIMMS 2007 . The paper outlines the main features of current science and mathematics education at Qatari schools, examines the performance of Qatari students on both national and international tests, and looks at enrollment trends in science programs at Qatar University, the only national university in the stat...

Research paper thumbnail of THE IMPORTANCE OF PRACTICAL ACTIVITIES IN SCHOOL SCIENCE: PERSPECTIVES OF INDEPENDENT SCHOOL TEACHERS IN QATARI SCHOOLS Ziad Said1, Heather Friesen2, Hiba Al-Ezzah1

This paper explores the way in which practical activities are perceived and carried out in Qatari... more This paper explores the way in which practical activities are perceived and carried out in Qatari schools, and identifies existing barriers and enablers for their implementation from the perspectives of science teachers. The study is based on a survey of 179 science teachers from nearly 50 different schools as well as interviews of 36 teachers representing primary, preparatory and secondary schools. The survey consists of 43 statements grouped into seven domains: Purpose of practical, barriers to effective delivery, time spent on practical, how practical sessions are delivered, how activities are assessed and what percentage weighting is allocated to practical from the total science grade, and what are the enablers that promote effective practical science delivery. Reliability statistical analysis generated a consistency within each of the above constructs with Cronbach's alpha ( ) values between 0.73 and 0.85 and values of 0.70-0.75 for the consistency between the constructs of...

Research paper thumbnail of Some Adsorption Characteristics of Sodium decyl and dodecyl Sulphates on the surface of Emulsifier-free Polymer Latex Particles

The adsorption characteristics of sodium decyl and dodecyl sulphates on polystyrene latex particl... more The adsorption characteristics of sodium decyl and dodecyl sulphates on polystyrene latex particles have been investigated. The study involves the addition of known amounts of the surfactant to an emulsifier-free latex, allowed to equilibrate at 33°C, and separating the two phases by a high speed centrifugation. The remaining concentration of the emulsifier is complexed with a solution of methylene blue and extracted by an organic solvent . the absorption of the organic phase is then measured at 610 nm. The adsorption isotherm is determined from the concentration profile from which the amount of emulsifier adsorbed is calculated. Knowing the average particle size, and consequently, number concentration of latex particles, allows the calculation of the moleculer area, Ag of the emulsifier in the saturated monolayer at the interface. This was found to be as 62A°2 for the decyl sulphate and 37A °2 for dodecyl sulphate in the presence of 0.1 M NaCl. The limiting molecular area, Ao were,...

Research paper thumbnail of Molecular-weight distributions in the thermally initiated emulsion polymerization of styrene

ABSTRACT In both thermal emulsion polymerization of styrene in the temperature range 60–80 °C, an... more ABSTRACT In both thermal emulsion polymerization of styrene in the temperature range 60–80 °C, and peroxodisulfate-initiated polymerization at 60 °C, weight-average to number-average molecular-weight ratios (M̄w/M̄n) approach 1,5 when potassium octadecanoate is used as emulsifier. A low activation energy for thermal initiation (≈66,0 kJ/mol) was deduced which may indicate a catalytic effect of the emulsifier during the thermal initiation process. Participation of the emulsifier is probably attributed to a transfer of one of two monomer radicals, produced thermally, to the emulsifier, with subsequent desorption to the aqueous phase, leaving one radical in the polymerization locus.

Research paper thumbnail of Possible evidence for the existence of a hairy layer at the surface of polymer latex particles

Polymer International, 1998

Research paper thumbnail of Saturation Swelling and the Seeded Emulsion Polymerisation of Styrene at High Ionic Strength

Polymer International, 1996

ABSTRACT The effects of adding inorganic electrolyte (below the critical coagulation concentratio... more ABSTRACT The effects of adding inorganic electrolyte (below the critical coagulation concentration) have been investigated in two systems for the emulsion polymerisation of styrene. In one system, potassium chloride, at different concentrations, was added at the end of interval I, using three different ionic emulsifiers: potassium octadecanoate which has a low critical micelle concentration (CMC), potassium dodecanoate and sodium dodecyl sulphate (SDS), which have moderately high CMC. A significant increase in the rate of polymerisation was observed in all cases even at the higher levels of electrolyte at which the rate is reduced if the electrolyte is added from the onset of polymerisation. In the second system, the effects of adding sodium chloride, in concentrations up to 0.2M, on the seeded emulsion polymerisation of styrene have been followed. A significant increase in the rate was observed as electrolyte level was increased, with no significant change in particle size. Saturation swelling measurements indicated a slight increase in monomer concentration inside the particles as electrolyte concentration was increased. Evaluation of the average number of free radicals per particle, n¯, by a steady state approach indicates an increase in the value of n¯ as electrolyte level is increased. The value of n¯ is below 0.5 but approaches this value at the highest electrolyte concentration. The increased surface area of the particles may account for this effect by increasing the capture efficiency of the radicals by the particles.

Research paper thumbnail of A reinvestigation of electrolyte effects in the emulsion polymerisation of styrene

Polymer International, 1994

ABSTRACT The effects of adding potassium chloride in concentrations below that required to coagul... more ABSTRACT The effects of adding potassium chloride in concentrations below that required to coagulate the latex to recips of emulsion polymerisation of styrene have been investigated using different concentrations of potassium octadecanoate, which has a low critical micelle concentration (CMC), and potassium dodecanoate, which has a moderately high CMC. At relatively high concentration of octadecanoate the final particle size is significantly increased; the rate of polymerisation is initially increased but later retarded. The effects of increasing micelle size and increased rate of coalescence are dominant. At lower concentration of this emulsifier, the rate is reduced from the onset of interval II. With dodecanoate, concentrations of electrolyte up to 0.3 M accelerate the rate. No significant change in the particle size was observed up to 0.2M electrolyte, thereafter it slightly increased. The increase in micellar concentration can only partially account for these effects. It is believed that the increase in the amount of solubilised monomer inside the micelles, and later inside the latex particles, and the resistance to coalescence (because of the favourable adsorption mechanism of this emulsifier) may account for these observations. With both emulsifiers, electrolyte reduces the induction period and latices with narrow particle size distributions are produced.

Research paper thumbnail of The effects of electrolyte concentration in the emulsion polymerization of styrene

Polymer, 1982

Using concentrations below that required to coagulate the latex, the effects of the addition of p... more Using concentrations below that required to coagulate the latex, the effects of the addition of potassium chloride on the emulsion polymerization of styrene have been investigated. When potassium decanoate (an emulsifier with a high critical micelle concentration (c.m.c.)) is used the increase in the concentration of micellar emulsifier and the decrease in the area occupied by an emulsifier molecule at the polymer/water interface are significant. When this is taken into account Gardon's equation for latex particle size reproduces the trend of the experimental results at the lower electrolyte concentrations. The agreement can be made quantitative by choosing alternative values for the propagation rate constant of styrene and the rate of radical formation from persulphate. With potassium octadecanoate (which has a low c.m.c.) and with potassium decanoate at the higher electrolyte concentrations these factors cannot account for the results observed.

Research paper thumbnail of Fluorescence probes as molecular weight detectors of polymers

Journal of Fluorescence, 1998

It is shown that the relative intensity of the twisted intramolecular charge transfer (TICT) band... more It is shown that the relative intensity of the twisted intramolecular charge transfer (TICT) band of ester and benzonitrile derivatives of dialkylaniline in polymethylmethacrylate polymer matrices of different molecular weights (MW) to increase with increasing MW of the polymer. Our results emphasis the role of local free volumes (mobility in the matrix cage) and focus attention on the role of the MW of the polymer on the fluorescence of various TICT probes. These observations are confirmed by the red edge effect and fluorescence decay results.

Research paper thumbnail of Development and Large-Scale Validation of an Instrument to Assess Arabic-Speaking Students' Attitudes Toward Science

This study is part of a large-scale project focused on 'Qatari students' Interest in, and... more This study is part of a large-scale project focused on 'Qatari students' Interest in, and Attitudes toward, Science' (QIAS). QIAS aimed to gauge Qatari student attitudes toward science in grades 3–12, examine factors that impact these attitudes, and assess the relationship between student attitudes and prevailing modes of science teaching in Qatari schools. This report details the development and validation of the 'Arabic-Speaking Students' Attitudes toward Science Survey' (ASSASS), which was specifically developed for the purposes of the QIAS project. The theories of reasoned action and planned behavior (TRAPB) [Ajzen, I., & Fishbein, M. (2005). The influence of attitudes on behavior. In D. Albarracín, B. T. Johnson, & M. P. Zanna (Eds.), The handbook of attitudes (pp. 173–221). Mahwah, NJ: Erlbaum] guided the instrument development. Development and validation of the ASSASS proceeded in 3 phases. First, a 10-member expert panel examined an initial pool of 74...

Research paper thumbnail of Assessing the Science Interest, Attitude, and Self-Efficacy of Qatari Students at the Preparatory, Secondary, and University Levels

Eurasia Journal of Mathematics, Science and Technology Education

A large sample (n = 1,799) of Qatari female and male students at the preparatory, secondary, and ... more A large sample (n = 1,799) of Qatari female and male students at the preparatory, secondary, and university levels responded to Likert items about their interest, attitude, and self-efficacy regarding science. The items were similar to those of TIMSS and PISA, but improved upon them in several ways. The findings suggest that Qatari students are positive in their interest, attitude, and self-efficacy, but not as positive as TIMSS and PISA report. The findings raise an important question: If the students' interest, attitude, and self-efficacy are positive, then why do the students have relatively low achievement scores on TIMSS and PISA? The answer may be the instructional methods and conditions of a developing educational system. The present findings have implications for all countries that use TIMSS and PISA, particularly those countries with developing educational systems, rapidly expanding economies, and an increasing need for students in science careers.

Research paper thumbnail of Teaching Style Differences between Male and Female Science Teachers in Qatari Schools: Possible Impact on Student Achievement

Eurasia Journal of Mathematics, Science and Technology Education

In Qatar's gender-segregated public schools, female students outperform male students in internat... more In Qatar's gender-segregated public schools, female students outperform male students in international science tests such as PISA and TIMMS. In contrast to the international trend for top performing countries, however, female students report lower levels of interest in science-based careers than males. One possible factor that may contribute to this discrepancy is the difference in teaching styles between female teachers and their male counterparts. In this paper we focus on results obtained from 105 classroom observations (39 males and 66 females) selected from 50 different public schools as part of two independent research projects to study the motivation factors and attitudes toward and interest in science among Qatari students. In addition, 40 semi-structured interviews of students, teachers and administrators were conducted. The observations were guided using an adopted Reformed Teaching Observation Protocol (RTOP) evaluation rubric consisting of 13 teaching traits which provides a standardized mean for detecting the degree to which science classroom instruction is reformed through a focus on Lesson Design, Content, Pedagogic Knowledge and classroom culture. Female teachers provided better delivery during theory classes, whereas male teachers demonstrated better performance in laboratory-based classes.

Research paper thumbnail of Comparing Likert Scale Functionality Across Culturally and Linguistically Diverse Groups in Science Education Research: an Illustration Using Qatari Students’ Responses to an Attitude Toward Science Survey

International Journal of Science and Mathematics Education

Surveying is a common methodology in science education research, including cross-national and cro... more Surveying is a common methodology in science education research, including cross-national and cross-cultural comparisons. The literature surrounding students' attitudes toward science, in particular, illustrates the prevalence of efforts to translate instruments with the eventual goal of comparing groups. This paper utilizes survey data from a nationally representative crosssectional study of Qatari students in grades 3 through 12 to frame a discussion around the adequacy and extent to which common adaptations allow comparisons to be made among linguistically or culturally different respondents. The analytic sample contained 2,615 students who responded to a previously validated 32-item instrument, 1,704 of whom completed the survey in Modern Standard Arabic and 911 in English. The purpose of using these data is to scrutinize variation in the performance of the instrument between groups of respondents as determined by language of survey completion and cultural heritage. Multi-group confirmatory factor analysis was employed to investigate issues of validity associated with the performance of the survey with each group, and to evaluate the appropriateness of using this instrument to make simultaneous comparisons across the distinct groups. Findings underscore the limitations of group comparability that may persist even when issues of translation and adaptation were heavily attended to during instrument development.

Research paper thumbnail of Science Education Reform in Qatar: Progress and Challenges

EURASIA Journal of Mathematics, Science & Technology Education

Science education reform in Qatar has had limited success. In the Trends in International Mathema... more Science education reform in Qatar has had limited success. In the Trends in International Mathematics and Science Study (TIMMS), Qatari 4th and 8th grade students have shown progress in science achievement, but they remain significantly below the international average. Also, in the Program for International Student Assessment (PISA), Qatari students have shown progress in science achievement, but they are again below the international average. To gain insight into what factors limit the students' science achievement, the School Science Teaching Inventory Questionnaire (SSTIQ) was administered to science coordinators and teachers in 24 independent schools in Qatar. The questionnaire results, in conjunction with interviews, indicated that science coordinators and teachers believed that a set of factors was responsible, and that low student motivation was the factor that was most responsible. Low student motivation was due, in part, to textbooks being overemphasized, and inquiry-based and problem-based methods being underemphasized. Based on these findings, recommendations for improving students' science achievement were provided.

Research paper thumbnail of The Impact of Long Teachers’ Training on Performance and Attitude Toward Science of Both Teachers and Students-The Case of Secondary School Teachers

INTED2017 Proceedings, 2017

Research paper thumbnail of Attitudes toward science among grades 3 through 12 Arab students in Qatar: findings from a cross-sectional national study

International Journal of Science Education, 2016

Research paper thumbnail of ‘Qatari Students’ Interest in Attitudes toward Science: the Impact of the Educational Reform on Science Education in Qatar

Qatar Foundation Annual Research Forum Proceedings, Dec 14, 2011

Research paper thumbnail of Qatari Students Performance, Interest In, and Attitude Towards Science and Mathematics

Despite the resources that have been invested in the educational reform in Qatar in the last few ... more Despite the resources that have been invested in the educational reform in Qatar in the last few years, no systematic study has been conducted to investigate the factors behind the disengagement and disinterest in science and mathematics in Qatari schools. This paper explores why the Qatari education reforms launched in 2003 as “Education for a New Era” have not reversed the significant decline observed over the past 15 years in the number of students studying mathematics and science at both secondary and tertiary levels of education although a significant relative progress has been observed in the recently published international results of TIMMS 2011 as compared to previous TIMMS 2007 . The paper outlines the main features of current science and mathematics education at Qatari schools, examines the performance of Qatari students on both national and international tests, and looks at enrollment trends in science programs at Qatar University, the only national university in the stat...

Research paper thumbnail of THE IMPORTANCE OF PRACTICAL ACTIVITIES IN SCHOOL SCIENCE: PERSPECTIVES OF INDEPENDENT SCHOOL TEACHERS IN QATARI SCHOOLS Ziad Said1, Heather Friesen2, Hiba Al-Ezzah1

This paper explores the way in which practical activities are perceived and carried out in Qatari... more This paper explores the way in which practical activities are perceived and carried out in Qatari schools, and identifies existing barriers and enablers for their implementation from the perspectives of science teachers. The study is based on a survey of 179 science teachers from nearly 50 different schools as well as interviews of 36 teachers representing primary, preparatory and secondary schools. The survey consists of 43 statements grouped into seven domains: Purpose of practical, barriers to effective delivery, time spent on practical, how practical sessions are delivered, how activities are assessed and what percentage weighting is allocated to practical from the total science grade, and what are the enablers that promote effective practical science delivery. Reliability statistical analysis generated a consistency within each of the above constructs with Cronbach's alpha ( ) values between 0.73 and 0.85 and values of 0.70-0.75 for the consistency between the constructs of...

Research paper thumbnail of Some Adsorption Characteristics of Sodium decyl and dodecyl Sulphates on the surface of Emulsifier-free Polymer Latex Particles

The adsorption characteristics of sodium decyl and dodecyl sulphates on polystyrene latex particl... more The adsorption characteristics of sodium decyl and dodecyl sulphates on polystyrene latex particles have been investigated. The study involves the addition of known amounts of the surfactant to an emulsifier-free latex, allowed to equilibrate at 33°C, and separating the two phases by a high speed centrifugation. The remaining concentration of the emulsifier is complexed with a solution of methylene blue and extracted by an organic solvent . the absorption of the organic phase is then measured at 610 nm. The adsorption isotherm is determined from the concentration profile from which the amount of emulsifier adsorbed is calculated. Knowing the average particle size, and consequently, number concentration of latex particles, allows the calculation of the moleculer area, Ag of the emulsifier in the saturated monolayer at the interface. This was found to be as 62A°2 for the decyl sulphate and 37A °2 for dodecyl sulphate in the presence of 0.1 M NaCl. The limiting molecular area, Ao were,...

Research paper thumbnail of Molecular-weight distributions in the thermally initiated emulsion polymerization of styrene

ABSTRACT In both thermal emulsion polymerization of styrene in the temperature range 60–80 °C, an... more ABSTRACT In both thermal emulsion polymerization of styrene in the temperature range 60–80 °C, and peroxodisulfate-initiated polymerization at 60 °C, weight-average to number-average molecular-weight ratios (M̄w/M̄n) approach 1,5 when potassium octadecanoate is used as emulsifier. A low activation energy for thermal initiation (≈66,0 kJ/mol) was deduced which may indicate a catalytic effect of the emulsifier during the thermal initiation process. Participation of the emulsifier is probably attributed to a transfer of one of two monomer radicals, produced thermally, to the emulsifier, with subsequent desorption to the aqueous phase, leaving one radical in the polymerization locus.

Research paper thumbnail of Possible evidence for the existence of a hairy layer at the surface of polymer latex particles

Polymer International, 1998

Research paper thumbnail of Saturation Swelling and the Seeded Emulsion Polymerisation of Styrene at High Ionic Strength

Polymer International, 1996

ABSTRACT The effects of adding inorganic electrolyte (below the critical coagulation concentratio... more ABSTRACT The effects of adding inorganic electrolyte (below the critical coagulation concentration) have been investigated in two systems for the emulsion polymerisation of styrene. In one system, potassium chloride, at different concentrations, was added at the end of interval I, using three different ionic emulsifiers: potassium octadecanoate which has a low critical micelle concentration (CMC), potassium dodecanoate and sodium dodecyl sulphate (SDS), which have moderately high CMC. A significant increase in the rate of polymerisation was observed in all cases even at the higher levels of electrolyte at which the rate is reduced if the electrolyte is added from the onset of polymerisation. In the second system, the effects of adding sodium chloride, in concentrations up to 0.2M, on the seeded emulsion polymerisation of styrene have been followed. A significant increase in the rate was observed as electrolyte level was increased, with no significant change in particle size. Saturation swelling measurements indicated a slight increase in monomer concentration inside the particles as electrolyte concentration was increased. Evaluation of the average number of free radicals per particle, n¯, by a steady state approach indicates an increase in the value of n¯ as electrolyte level is increased. The value of n¯ is below 0.5 but approaches this value at the highest electrolyte concentration. The increased surface area of the particles may account for this effect by increasing the capture efficiency of the radicals by the particles.

Research paper thumbnail of A reinvestigation of electrolyte effects in the emulsion polymerisation of styrene

Polymer International, 1994

ABSTRACT The effects of adding potassium chloride in concentrations below that required to coagul... more ABSTRACT The effects of adding potassium chloride in concentrations below that required to coagulate the latex to recips of emulsion polymerisation of styrene have been investigated using different concentrations of potassium octadecanoate, which has a low critical micelle concentration (CMC), and potassium dodecanoate, which has a moderately high CMC. At relatively high concentration of octadecanoate the final particle size is significantly increased; the rate of polymerisation is initially increased but later retarded. The effects of increasing micelle size and increased rate of coalescence are dominant. At lower concentration of this emulsifier, the rate is reduced from the onset of interval II. With dodecanoate, concentrations of electrolyte up to 0.3 M accelerate the rate. No significant change in the particle size was observed up to 0.2M electrolyte, thereafter it slightly increased. The increase in micellar concentration can only partially account for these effects. It is believed that the increase in the amount of solubilised monomer inside the micelles, and later inside the latex particles, and the resistance to coalescence (because of the favourable adsorption mechanism of this emulsifier) may account for these observations. With both emulsifiers, electrolyte reduces the induction period and latices with narrow particle size distributions are produced.

Research paper thumbnail of The effects of electrolyte concentration in the emulsion polymerization of styrene

Polymer, 1982

Using concentrations below that required to coagulate the latex, the effects of the addition of p... more Using concentrations below that required to coagulate the latex, the effects of the addition of potassium chloride on the emulsion polymerization of styrene have been investigated. When potassium decanoate (an emulsifier with a high critical micelle concentration (c.m.c.)) is used the increase in the concentration of micellar emulsifier and the decrease in the area occupied by an emulsifier molecule at the polymer/water interface are significant. When this is taken into account Gardon's equation for latex particle size reproduces the trend of the experimental results at the lower electrolyte concentrations. The agreement can be made quantitative by choosing alternative values for the propagation rate constant of styrene and the rate of radical formation from persulphate. With potassium octadecanoate (which has a low c.m.c.) and with potassium decanoate at the higher electrolyte concentrations these factors cannot account for the results observed.

Research paper thumbnail of Fluorescence probes as molecular weight detectors of polymers

Journal of Fluorescence, 1998

It is shown that the relative intensity of the twisted intramolecular charge transfer (TICT) band... more It is shown that the relative intensity of the twisted intramolecular charge transfer (TICT) band of ester and benzonitrile derivatives of dialkylaniline in polymethylmethacrylate polymer matrices of different molecular weights (MW) to increase with increasing MW of the polymer. Our results emphasis the role of local free volumes (mobility in the matrix cage) and focus attention on the role of the MW of the polymer on the fluorescence of various TICT probes. These observations are confirmed by the red edge effect and fluorescence decay results.

Research paper thumbnail of Development and Large-Scale Validation of an Instrument to Assess Arabic-Speaking Students' Attitudes Toward Science

This study is part of a large-scale project focused on 'Qatari students' Interest in, and... more This study is part of a large-scale project focused on 'Qatari students' Interest in, and Attitudes toward, Science' (QIAS). QIAS aimed to gauge Qatari student attitudes toward science in grades 3–12, examine factors that impact these attitudes, and assess the relationship between student attitudes and prevailing modes of science teaching in Qatari schools. This report details the development and validation of the 'Arabic-Speaking Students' Attitudes toward Science Survey' (ASSASS), which was specifically developed for the purposes of the QIAS project. The theories of reasoned action and planned behavior (TRAPB) [Ajzen, I., & Fishbein, M. (2005). The influence of attitudes on behavior. In D. Albarracín, B. T. Johnson, & M. P. Zanna (Eds.), The handbook of attitudes (pp. 173–221). Mahwah, NJ: Erlbaum] guided the instrument development. Development and validation of the ASSASS proceeded in 3 phases. First, a 10-member expert panel examined an initial pool of 74...