Debarshi Dasgupta - Academia.edu (original) (raw)

Papers by Debarshi Dasgupta

Macromolecules, 2018

The cooperativity of van der Waals interactions in biomolecules and supramolecular assemblies has... more The cooperativity of van der Waals interactions in biomolecules and supramolecular assemblies has drawn significant scientific attention due to its offering of seamless opportunities to generate new materials. However, the potential of such cooperativity in synthetic polymers has not yet been explored. In this study, we demonstrate a strategy to achieve cooperativity via enhancement of weak interactions in a designed siloxane copolymer. Segmentation of siloxane copolymer with specific alkyl chain length (C18) induces cooperativity in van der Waals interaction among the alkyl chains, resulting in interdigitated as well as end-to-end packing. The cooperativity of van der Waals interactions is also evident by an excess melting enthalpy of ΔH = 1.86 kJ/mol in the designed block siloxane copolymer as compared to its control counterpart, i.e., a compositionally similar random siloxane copolymer. The dynamic relationship of cooperativity and physical properties is established by various analytical tools and further substantiated by disturbing the regularity of the block segments using a trace amount (1 per 99 octadecyl units) of a dissimilar alkyl chain as "dopant".

Macromolecular Chemistry and Physics, 2013

ABSTRACT The mechanisms responsible for the physical gelation of polymers and of organogelators a... more ABSTRACT The mechanisms responsible for the physical gelation of polymers and of organogelators are discussed and compared. For polymers, the prerequisite for obtaining fibrillar thermoreversible gels is the impediment of chain folding. This occurs when polymers take on a worm-like chain conformation with a large persistence length. This property can be intrinsic to the polymer, such as agarose, or can be obtained by the occurrence of polymer-solvent molecular compounds, as is the case for stereoregular polymers. For organogels, it is suggested that the mechanism for producing fibrils involves the much faster growth of one face of the organogel crystal structure with respect to the other two, which can be enhanced via specific interactions with the solvent, something reminiscent of molecular compounds.

Macromolecular Symposia, Nov 1, 2008

ABSTRACT The thermodynamics of gelation of poly(vinylidene fluoride)(PVF2) with camphor (CP) and ... more ABSTRACT The thermodynamics of gelation of poly(vinylidene fluoride)(PVF2) with camphor (CP) and ethylene carbonate (EC) suggest polymer-solvent compound formation. The presence of solvent molecules in the polymer crystalline phase of the gel is accordingly shown by wide angle X-ray diffraction studies. The dried gels exhibit porous network morphology. Thermoreversible gel of PVF2 in diethyl azelate is also exploited to create multiporous polymer foam. Porosity measurements with the dried PVF2 gels using Mercury intrusion porosimetry and nitrogen sorption ensure the presence of macro and mesopores in the same matrix although the mesoporosity in dried PVF2-CP gels strongly depend on method of drying.

Langmuir, Apr 1, 2009

This paper reports on experiments intended for investigating the feasibility of preparing hybrid ... more This paper reports on experiments intended for investigating the feasibility of preparing hybrid thermoreversible gels from covalent polymers and noncovalent self-assembling pi-conjugated molecules. The formation and the degree of dispersion of these hybrid gels have been studied with polystyrenes of various tacticities and oligo(p-phenylenevinylene) molecules (OPV) in different nonpolar organic solvents. Detailed investigations of the systems have been carried out by DSC, SAXS, and AFM. It is shown that no liquid-liquid phase separation is involved, indicating that the systems are highly compatible, and that the growth of one type of gel does not interfere with the other. These studies reveal that the resultant hybrid gels are composed of the intermingled fibrillar architectures of both gels.

Soft Matter, 2012

ABSTRACT In this paper we again assess the role played by the solvent type in the organogelation ... more ABSTRACT In this paper we again assess the role played by the solvent type in the organogelation process of photo/electroactive oligo (para-phenylene vinylene) (OPV) molecules . In this aim we have investigated gelation in benzyl alcohol, a polar solvent, and trans-decahydronaphthalene, an apolar solvent. Several techniques have been used: DSC, SEM, AFM, TEM, X-ray diffraction, UV-vis, and fluorometry. We have observed that the gel thermodynamics (T–C phase diagram), morphologies, molecular order, and optical properties differ considerably with the solvent type. The results are discussed by considering the interaction of the solvent with the different moieties of the OPV molecule. The reason why fibrils are obtained instead of 3-D crystals is also considered on the basis of micro-diffraction experiments performed by electron microscopy on finite aggregates.

Soft Matter, 2011

ABSTRACT This paper reports a study on the gelation habits of organogels prepared in benzyl alcoh... more ABSTRACT This paper reports a study on the gelation habits of organogels prepared in benzyl alcohol from derivatives of oligo(p-phenylene vinylene) (OPV) bearing C16H33 aliphatic wings and a series of end groups on the backbone. Significant differences are observed based on whether or not these end groups can establish hydrogen bonds with adjacent OPV molecules or with the solvent. It is particularly shown that the fibril structure, the morphology and the molecular organization not only depend upon the aliphatic wings and/or the π–π interactions of the backbones but equally on the nature of these end groups. Evidence highlighting a homogeneous nucleation process for gel formation are also presented and discussed. Discrepancies with thermoreversible gels of covalent polymers are also stressed.

Soft Matter, 2010

This paper examines the possibility of sheathing polymer nanofibrils, prepared from a thermorever... more This paper examines the possibility of sheathing polymer nanofibrils, prepared from a thermoreversible gel, by nanotubules, obtained through self-assembly of a complex ester. The method for preparing this hybrid system consists of cooling ternary solutions until gelation is achieved. The sheathing mechanism most probably occurs through heterogeneous nucleation: polymer fibrils act as heterogeneous nuclei, and so trigger the growth of nanotubules around them. The occurrence of the sheathing process is investigated by DSC, AFM, SAXS and SANS. In the latter case, the contrast variation method is used. ; Fax: +33(0) 476547203; Tel: +33 476037603 † Electronic supplementary information (ESI) available: Supplementary figs 1 and 2. See

Soft Matter, 2011

ABSTRACT We have investigated the decisive role of the solvent type in the gelation of an oligo(p... more ABSTRACT We have investigated the decisive role of the solvent type in the gelation of an oligo(p-phenylene vinylene) molecule with OH functions on the terminal groups (OPVOH). We show that gels of “hub-like” morphology are obtained with benzyl alcohol, a solvent that mimics the chemical structure of the terminal groups, whereas a “randomly dispersed” morphology is obtained with trans-decahydronaphthalene and with benzyl methyl ether, a solvent very similar to benzyl alcohol except that the hydrogen of the OH function has been replaced by a CH3group. Also, the thermodynamic behaviour, gel formation and gel melting are similar for benzyl methyl ether and trans-decahydronaphthalene but are significantly different in benzyl alcohol: the gel melting point is higher, and so is the melting enthalpy. Extrapolation of this parameter to 100% OPVOH gives a value significantly higher than that directly measured on pure OPVOH. Molecular organization as studied by X-ray diffraction and fluorescence properties follow the same trend. The occurrence of a molecular compound between OPVOH and benzyl alcohol is contemplated in an attempt to account for these outcomes.

Macromolecules, 2007

Extraction of camphor from poly(vinylidene fluoride) (PVF 2 )-camphor systems prepared at two dif... more Extraction of camphor from poly(vinylidene fluoride) (PVF 2 )-camphor systems prepared at two different compositions (10% and 40% w/w) indicates multiporosity. Two methods were applied for the extraction process : (i) by applying vacuum (10 -3 mmHg) (VD) and (ii) by replacement of the host matrix by cyclohexane followed by drying (CD). The morphology, porosity, structure, and thermal properties of these samples were studied by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), mercury intrusion porosimetry (MIP), nitrogen adsorption porosimetry (BET adsorption isotherm), wide-angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC). High-pressure (20-34 000 psi) MIP histograms for all the samples indicate the presence of meso-and macropores, and low-pressure (0.5-50 psi) MIP histograms indicate the presence of large macropores in the samples. Analysis of pore size distribution from nitrogen adsorption studies by the Horvath-Kawazoe (HK) and Barett-Joyner-Halenda (BJH) models indicates the presence of micro-and mesopores produced from single, double, or multiple camphor layers between the PVF 2 strands particularly for CD samples. Pore diameter values nearly equal to the model value of 2:1 and 4:1 compounds were detected for both the single-and double-camphor layer complexation in the dried samples. However, vacuumdried samples (P-10VD and P-40VD, the numerical numbers indicate weight percent of polymer in the gel from where it is derived) do not exhibit existence of any micropore. Mesopores were observed in all the samples although the pore size distribution is broader in VD samples than that in CD samples. The macropores are larger in size in the P-10VD samples compared to that in P-10CD samples, but in the P-40VD sample the macropore size is either reduced or lost. The hysteresis loops indicate the presence of interconnectivity between the pores, and it is lesser in the vacuum-dried samples. The surface area has greatly decreased in VD samples compared to that in CD samples. This suggests that on vacuum drying a large amount of porosity and interconnectivity is lost than those of CD samples. A schematic model is presented for the loss of porosity in vacuum drying. The crystal structure is independent of drying method, and the melting point of the porous surface increases in VD samples compared to that in CD samples, indicating that thicker porous surface is produced on vacuum drying. The collapsing of pores decreases the porosity in VD samples due to mechanical jerking. Honeycomb-type pores are observed in the P-40CD sample, and the faster crystallization rate of camphor than that of PVF 2 has been attributed to the honeycomb-type pore formation. The sheetlike morphology of PVF 2 obtained from dried dilute gels has been attributed to its crystallization through the niches of camphor crystals followed by extraction of camphor.

Macromolecules, 2005

Poly(vinylidene fluoride) (PVF2)-camphor systems have been investigated in concentrations ranging... more Poly(vinylidene fluoride) (PVF2)-camphor systems have been investigated in concentrations ranging from WPVF2 ) 0 to 1 (w/w). The temperature-concentration phase diagram suggests the formation of two different polymer-solvent compounds of an incongruently melting type (C1 and C2), a eutectic transition, and a metatectic transition. The data related to the melting enthalpy of the different firstorder events provide one with stoichiometries of 1/2 and 1/4 for compound C1 and compound C2, respectively (number of camphor molecules per PVF2 monomer). Time-resolved X-ray experiments carried out as a function of temperature also support the existence of two different compounds. The optical microscopy shows an abrupt change of texture with increasing temperature. The morphology as observed from SEM after drying under vacuum shows tubular, porous structures for concentration below the stoichiometric composition of compound C 2 and the appearance of spherulites above.

Macromolecules, 2008

Poly(vinylidene fluoride) (PVF 2 ) produces a thermoreversible gel with the important solvent, et... more Poly(vinylidene fluoride) (PVF 2 ) produces a thermoreversible gel with the important solvent, ethylene carbonate, which is used as a dispersing medium in a lithium ion battery. This is evidenced from the fibrillar network morphology and reversible first-order phase transition of the gels. The invariance of the storage and loss modulus with frequency at lower temperatures (e110°C) and the existence of a crossover point between them at higher temperatures further supports thermoreversible gel formation in the system. Solvent subtracted FTIR spectra of the gels indicate formation of a polymorph, which is retained even after drying using cyclohexane as a guest solvent. The wide-angle x-ray scattering (WAXS) diffractogram of the dried gel also indicates formation of the piezoelectric polymorph, giving a first time report of thermoreversible piezoelectric gel formation. The temperature-concentration phase diagram in conjunction with Tamman's plot indicates the presence of a polymersolvent molecular compound whose stoichiometry is around 1.2 solvent molecules/monomer unit. The presence of eutectic and metatectic transitions in the PVF 2ethylene carbonate (EC) system is also evidenced from the phase diagram. Time-resolved X-ray diffraction patterns also show a new peak at q )13.15 nm -1 which is assigned to the molecular compound on the basis of a possible crystalline lattice. Molecular modeling using molecular mechanics calculations with the MMX program supports polymer-solvent complex formation. It also indicates that electrostatic and H-bonding forces are operating side by side on the carbon skeleton fixing the all trans chain conformation of PVF 2 in the gel.

Macromolecules, 2006

ABSTRACT The poly( vinylidene fluoride) (PVF2)-ethyl acetoacetate (EAA) system produces polymer-s... more ABSTRACT The poly( vinylidene fluoride) (PVF2)-ethyl acetoacetate (EAA) system produces polymer-solvent compounds. The temperature-concentration phase diagram and the Tamman's diagram indicate that the polymersolvent complexes are of two different types which are stable in different temperature regions; one is a congruently melting compound while the other is of the singular type. Also, a metatectic-like behavior is observed due to the peculiar melting behavior of PVF2. The morphology of the compounds resembles a "crumpled cloth" network, with the probable presence of chain-folded lamellae. SAXS study indicates presence of chain-folded lamellae of lamellar thickness 8 nm in the PVF2-EAA systems. FTIR and WAXS spectra indicate formation of R polymorphic structure of PVF2, and they are consistent with the occurrence of compounds. Indeed, two new X-ray diffraction peaks are observed for the system at 2 theta = 22.2 degrees and 24.0 degrees near the polymer- solvent complex stoichiometric composition (W-PVF2 = 0.33). The FTIR spectrum also shows a new peak at 592 cm(-1) for the complex formation at the stoichiometric composition. Molecular modeling using the MMX program supports the polymer- solvent complexation in this system.

Macromolecular Symposia, 2006

Macromolecular Symposia, 2005

Macromolecular Symposia, 2005

Thermoreversible gelation of a copolymer, poly(vinylidene fluoride-co-chlorotrifluoroethylene), h... more Thermoreversible gelation of a copolymer, poly(vinylidene fluoride-co-chlorotrifluoroethylene), has been studied in a series of aromatic diesters (phthalates) with varying aliphatic chain length, n. The gelation rate gradually increases ...

Macromolecular Symposia, 2007

... [1] BP Santora, MP Gagne, KG Moloy, NS Redu, Macromolecules 2001, 34, 658. [2] A. Corma, Chem... more ... [1] BP Santora, MP Gagne, KG Moloy, NS Redu, Macromolecules 2001, 34, 658. [2] A. Corma, Chem. Rev. 1997, 97, 2373. ... 1985, 57, 603. [8] D. Dasgupta, AK Nandi, Macromolecules 2005, 38, 6504. [9] D. Dasgupta, AK Nandi, Macromol. Symp. 2006, 222, 81. ...

Journal of the American Chemical Society, 2013

A nanoporous smectic liquid crystalline polymer network has been exploited to fabricate photo pat... more A nanoporous smectic liquid crystalline polymer network has been exploited to fabricate photo patternable organic−inorganic hybrid materials, wherein, the nanoporous channels control the diameter and orientational order of the silver nanoparticles.

Beilstein Journal of Organic Chemistry, 2010

A chiral organogelator has been synthesized that can be racemized and self-assembled in apolar so... more A chiral organogelator has been synthesized that can be racemized and self-assembled in apolar solvents whilst at higher concentrations organogels are formed. Field emission scanning and transmission electron microscopy revealed the formation of bundle fibrils that are able to gelate the solvent. 1 H NMR studies showed hydrogen-bond interactions between the peptide head groups of neighbouring organogelator molecules. The enantiomerically pure organogelator can be racemized by the base DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) as was evident from chiral high-performance liquid chromatography analysis.

Macromolecules, 2018

The cooperativity of van der Waals interactions in biomolecules and supramolecular assemblies has... more The cooperativity of van der Waals interactions in biomolecules and supramolecular assemblies has drawn significant scientific attention due to its offering of seamless opportunities to generate new materials. However, the potential of such cooperativity in synthetic polymers has not yet been explored. In this study, we demonstrate a strategy to achieve cooperativity via enhancement of weak interactions in a designed siloxane copolymer. Segmentation of siloxane copolymer with specific alkyl chain length (C18) induces cooperativity in van der Waals interaction among the alkyl chains, resulting in interdigitated as well as end-to-end packing. The cooperativity of van der Waals interactions is also evident by an excess melting enthalpy of ΔH = 1.86 kJ/mol in the designed block siloxane copolymer as compared to its control counterpart, i.e., a compositionally similar random siloxane copolymer. The dynamic relationship of cooperativity and physical properties is established by various analytical tools and further substantiated by disturbing the regularity of the block segments using a trace amount (1 per 99 octadecyl units) of a dissimilar alkyl chain as "dopant".

Macromolecular Chemistry and Physics, 2013

ABSTRACT The mechanisms responsible for the physical gelation of polymers and of organogelators a... more ABSTRACT The mechanisms responsible for the physical gelation of polymers and of organogelators are discussed and compared. For polymers, the prerequisite for obtaining fibrillar thermoreversible gels is the impediment of chain folding. This occurs when polymers take on a worm-like chain conformation with a large persistence length. This property can be intrinsic to the polymer, such as agarose, or can be obtained by the occurrence of polymer-solvent molecular compounds, as is the case for stereoregular polymers. For organogels, it is suggested that the mechanism for producing fibrils involves the much faster growth of one face of the organogel crystal structure with respect to the other two, which can be enhanced via specific interactions with the solvent, something reminiscent of molecular compounds.

Macromolecular Symposia, Nov 1, 2008

ABSTRACT The thermodynamics of gelation of poly(vinylidene fluoride)(PVF2) with camphor (CP) and ... more ABSTRACT The thermodynamics of gelation of poly(vinylidene fluoride)(PVF2) with camphor (CP) and ethylene carbonate (EC) suggest polymer-solvent compound formation. The presence of solvent molecules in the polymer crystalline phase of the gel is accordingly shown by wide angle X-ray diffraction studies. The dried gels exhibit porous network morphology. Thermoreversible gel of PVF2 in diethyl azelate is also exploited to create multiporous polymer foam. Porosity measurements with the dried PVF2 gels using Mercury intrusion porosimetry and nitrogen sorption ensure the presence of macro and mesopores in the same matrix although the mesoporosity in dried PVF2-CP gels strongly depend on method of drying.

Langmuir, Apr 1, 2009

This paper reports on experiments intended for investigating the feasibility of preparing hybrid ... more This paper reports on experiments intended for investigating the feasibility of preparing hybrid thermoreversible gels from covalent polymers and noncovalent self-assembling pi-conjugated molecules. The formation and the degree of dispersion of these hybrid gels have been studied with polystyrenes of various tacticities and oligo(p-phenylenevinylene) molecules (OPV) in different nonpolar organic solvents. Detailed investigations of the systems have been carried out by DSC, SAXS, and AFM. It is shown that no liquid-liquid phase separation is involved, indicating that the systems are highly compatible, and that the growth of one type of gel does not interfere with the other. These studies reveal that the resultant hybrid gels are composed of the intermingled fibrillar architectures of both gels.

Soft Matter, 2012

ABSTRACT In this paper we again assess the role played by the solvent type in the organogelation ... more ABSTRACT In this paper we again assess the role played by the solvent type in the organogelation process of photo/electroactive oligo (para-phenylene vinylene) (OPV) molecules . In this aim we have investigated gelation in benzyl alcohol, a polar solvent, and trans-decahydronaphthalene, an apolar solvent. Several techniques have been used: DSC, SEM, AFM, TEM, X-ray diffraction, UV-vis, and fluorometry. We have observed that the gel thermodynamics (T–C phase diagram), morphologies, molecular order, and optical properties differ considerably with the solvent type. The results are discussed by considering the interaction of the solvent with the different moieties of the OPV molecule. The reason why fibrils are obtained instead of 3-D crystals is also considered on the basis of micro-diffraction experiments performed by electron microscopy on finite aggregates.

Soft Matter, 2011

ABSTRACT This paper reports a study on the gelation habits of organogels prepared in benzyl alcoh... more ABSTRACT This paper reports a study on the gelation habits of organogels prepared in benzyl alcohol from derivatives of oligo(p-phenylene vinylene) (OPV) bearing C16H33 aliphatic wings and a series of end groups on the backbone. Significant differences are observed based on whether or not these end groups can establish hydrogen bonds with adjacent OPV molecules or with the solvent. It is particularly shown that the fibril structure, the morphology and the molecular organization not only depend upon the aliphatic wings and/or the π–π interactions of the backbones but equally on the nature of these end groups. Evidence highlighting a homogeneous nucleation process for gel formation are also presented and discussed. Discrepancies with thermoreversible gels of covalent polymers are also stressed.

Soft Matter, 2010

This paper examines the possibility of sheathing polymer nanofibrils, prepared from a thermorever... more This paper examines the possibility of sheathing polymer nanofibrils, prepared from a thermoreversible gel, by nanotubules, obtained through self-assembly of a complex ester. The method for preparing this hybrid system consists of cooling ternary solutions until gelation is achieved. The sheathing mechanism most probably occurs through heterogeneous nucleation: polymer fibrils act as heterogeneous nuclei, and so trigger the growth of nanotubules around them. The occurrence of the sheathing process is investigated by DSC, AFM, SAXS and SANS. In the latter case, the contrast variation method is used. ; Fax: +33(0) 476547203; Tel: +33 476037603 † Electronic supplementary information (ESI) available: Supplementary figs 1 and 2. See

Soft Matter, 2011

ABSTRACT We have investigated the decisive role of the solvent type in the gelation of an oligo(p... more ABSTRACT We have investigated the decisive role of the solvent type in the gelation of an oligo(p-phenylene vinylene) molecule with OH functions on the terminal groups (OPVOH). We show that gels of “hub-like” morphology are obtained with benzyl alcohol, a solvent that mimics the chemical structure of the terminal groups, whereas a “randomly dispersed” morphology is obtained with trans-decahydronaphthalene and with benzyl methyl ether, a solvent very similar to benzyl alcohol except that the hydrogen of the OH function has been replaced by a CH3group. Also, the thermodynamic behaviour, gel formation and gel melting are similar for benzyl methyl ether and trans-decahydronaphthalene but are significantly different in benzyl alcohol: the gel melting point is higher, and so is the melting enthalpy. Extrapolation of this parameter to 100% OPVOH gives a value significantly higher than that directly measured on pure OPVOH. Molecular organization as studied by X-ray diffraction and fluorescence properties follow the same trend. The occurrence of a molecular compound between OPVOH and benzyl alcohol is contemplated in an attempt to account for these outcomes.

Macromolecules, 2007

Extraction of camphor from poly(vinylidene fluoride) (PVF 2 )-camphor systems prepared at two dif... more Extraction of camphor from poly(vinylidene fluoride) (PVF 2 )-camphor systems prepared at two different compositions (10% and 40% w/w) indicates multiporosity. Two methods were applied for the extraction process : (i) by applying vacuum (10 -3 mmHg) (VD) and (ii) by replacement of the host matrix by cyclohexane followed by drying (CD). The morphology, porosity, structure, and thermal properties of these samples were studied by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), mercury intrusion porosimetry (MIP), nitrogen adsorption porosimetry (BET adsorption isotherm), wide-angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC). High-pressure (20-34 000 psi) MIP histograms for all the samples indicate the presence of meso-and macropores, and low-pressure (0.5-50 psi) MIP histograms indicate the presence of large macropores in the samples. Analysis of pore size distribution from nitrogen adsorption studies by the Horvath-Kawazoe (HK) and Barett-Joyner-Halenda (BJH) models indicates the presence of micro-and mesopores produced from single, double, or multiple camphor layers between the PVF 2 strands particularly for CD samples. Pore diameter values nearly equal to the model value of 2:1 and 4:1 compounds were detected for both the single-and double-camphor layer complexation in the dried samples. However, vacuumdried samples (P-10VD and P-40VD, the numerical numbers indicate weight percent of polymer in the gel from where it is derived) do not exhibit existence of any micropore. Mesopores were observed in all the samples although the pore size distribution is broader in VD samples than that in CD samples. The macropores are larger in size in the P-10VD samples compared to that in P-10CD samples, but in the P-40VD sample the macropore size is either reduced or lost. The hysteresis loops indicate the presence of interconnectivity between the pores, and it is lesser in the vacuum-dried samples. The surface area has greatly decreased in VD samples compared to that in CD samples. This suggests that on vacuum drying a large amount of porosity and interconnectivity is lost than those of CD samples. A schematic model is presented for the loss of porosity in vacuum drying. The crystal structure is independent of drying method, and the melting point of the porous surface increases in VD samples compared to that in CD samples, indicating that thicker porous surface is produced on vacuum drying. The collapsing of pores decreases the porosity in VD samples due to mechanical jerking. Honeycomb-type pores are observed in the P-40CD sample, and the faster crystallization rate of camphor than that of PVF 2 has been attributed to the honeycomb-type pore formation. The sheetlike morphology of PVF 2 obtained from dried dilute gels has been attributed to its crystallization through the niches of camphor crystals followed by extraction of camphor.

Macromolecules, 2005

Poly(vinylidene fluoride) (PVF2)-camphor systems have been investigated in concentrations ranging... more Poly(vinylidene fluoride) (PVF2)-camphor systems have been investigated in concentrations ranging from WPVF2 ) 0 to 1 (w/w). The temperature-concentration phase diagram suggests the formation of two different polymer-solvent compounds of an incongruently melting type (C1 and C2), a eutectic transition, and a metatectic transition. The data related to the melting enthalpy of the different firstorder events provide one with stoichiometries of 1/2 and 1/4 for compound C1 and compound C2, respectively (number of camphor molecules per PVF2 monomer). Time-resolved X-ray experiments carried out as a function of temperature also support the existence of two different compounds. The optical microscopy shows an abrupt change of texture with increasing temperature. The morphology as observed from SEM after drying under vacuum shows tubular, porous structures for concentration below the stoichiometric composition of compound C 2 and the appearance of spherulites above.

Macromolecules, 2008

Poly(vinylidene fluoride) (PVF 2 ) produces a thermoreversible gel with the important solvent, et... more Poly(vinylidene fluoride) (PVF 2 ) produces a thermoreversible gel with the important solvent, ethylene carbonate, which is used as a dispersing medium in a lithium ion battery. This is evidenced from the fibrillar network morphology and reversible first-order phase transition of the gels. The invariance of the storage and loss modulus with frequency at lower temperatures (e110°C) and the existence of a crossover point between them at higher temperatures further supports thermoreversible gel formation in the system. Solvent subtracted FTIR spectra of the gels indicate formation of a polymorph, which is retained even after drying using cyclohexane as a guest solvent. The wide-angle x-ray scattering (WAXS) diffractogram of the dried gel also indicates formation of the piezoelectric polymorph, giving a first time report of thermoreversible piezoelectric gel formation. The temperature-concentration phase diagram in conjunction with Tamman's plot indicates the presence of a polymersolvent molecular compound whose stoichiometry is around 1.2 solvent molecules/monomer unit. The presence of eutectic and metatectic transitions in the PVF 2ethylene carbonate (EC) system is also evidenced from the phase diagram. Time-resolved X-ray diffraction patterns also show a new peak at q )13.15 nm -1 which is assigned to the molecular compound on the basis of a possible crystalline lattice. Molecular modeling using molecular mechanics calculations with the MMX program supports polymer-solvent complex formation. It also indicates that electrostatic and H-bonding forces are operating side by side on the carbon skeleton fixing the all trans chain conformation of PVF 2 in the gel.

Macromolecules, 2006

ABSTRACT The poly( vinylidene fluoride) (PVF2)-ethyl acetoacetate (EAA) system produces polymer-s... more ABSTRACT The poly( vinylidene fluoride) (PVF2)-ethyl acetoacetate (EAA) system produces polymer-solvent compounds. The temperature-concentration phase diagram and the Tamman's diagram indicate that the polymersolvent complexes are of two different types which are stable in different temperature regions; one is a congruently melting compound while the other is of the singular type. Also, a metatectic-like behavior is observed due to the peculiar melting behavior of PVF2. The morphology of the compounds resembles a "crumpled cloth" network, with the probable presence of chain-folded lamellae. SAXS study indicates presence of chain-folded lamellae of lamellar thickness 8 nm in the PVF2-EAA systems. FTIR and WAXS spectra indicate formation of R polymorphic structure of PVF2, and they are consistent with the occurrence of compounds. Indeed, two new X-ray diffraction peaks are observed for the system at 2 theta = 22.2 degrees and 24.0 degrees near the polymer- solvent complex stoichiometric composition (W-PVF2 = 0.33). The FTIR spectrum also shows a new peak at 592 cm(-1) for the complex formation at the stoichiometric composition. Molecular modeling using the MMX program supports the polymer- solvent complexation in this system.

Macromolecular Symposia, 2006

Macromolecular Symposia, 2005

Macromolecular Symposia, 2005

Thermoreversible gelation of a copolymer, poly(vinylidene fluoride-co-chlorotrifluoroethylene), h... more Thermoreversible gelation of a copolymer, poly(vinylidene fluoride-co-chlorotrifluoroethylene), has been studied in a series of aromatic diesters (phthalates) with varying aliphatic chain length, n. The gelation rate gradually increases ...

Macromolecular Symposia, 2007

... [1] BP Santora, MP Gagne, KG Moloy, NS Redu, Macromolecules 2001, 34, 658. [2] A. Corma, Chem... more ... [1] BP Santora, MP Gagne, KG Moloy, NS Redu, Macromolecules 2001, 34, 658. [2] A. Corma, Chem. Rev. 1997, 97, 2373. ... 1985, 57, 603. [8] D. Dasgupta, AK Nandi, Macromolecules 2005, 38, 6504. [9] D. Dasgupta, AK Nandi, Macromol. Symp. 2006, 222, 81. ...

Journal of the American Chemical Society, 2013

A nanoporous smectic liquid crystalline polymer network has been exploited to fabricate photo pat... more A nanoporous smectic liquid crystalline polymer network has been exploited to fabricate photo patternable organic−inorganic hybrid materials, wherein, the nanoporous channels control the diameter and orientational order of the silver nanoparticles.

Beilstein Journal of Organic Chemistry, 2010

A chiral organogelator has been synthesized that can be racemized and self-assembled in apolar so... more A chiral organogelator has been synthesized that can be racemized and self-assembled in apolar solvents whilst at higher concentrations organogels are formed. Field emission scanning and transmission electron microscopy revealed the formation of bundle fibrils that are able to gelate the solvent. 1 H NMR studies showed hydrogen-bond interactions between the peptide head groups of neighbouring organogelator molecules. The enantiomerically pure organogelator can be racemized by the base DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) as was evident from chiral high-performance liquid chromatography analysis.