Water-Resistant Poly(vinyl alcohol)-Silica Hybrids through Sol-Gel Processing (original) (raw)
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Structural analysis of poly(dimethylsiloxane) modified silica xerogels
Journal of Non-crystalline Solids, 1999
A new type of inorganic-organic hybrid material incorporating poly(dimethylsiloxane) (PDMS) in tetraethoxysilane (TEOS) based glassy gels has been produced by a sol±gel process. SAXS and SEM studies indicate that these PDMS modi®ed silica xerogels possess multiple size-scale morphologies, ranging from # Angstroms to micrometers. The multiple-level hybrid materials show improved structural integrity relative to pure sol±gel glasses (xerogels). The eect of reaction time, water content, as well as content and molecular weight of PDMS on the structure of such materials were studied. These processing variables aect the relative rates of hydrolysis and condensation reactions, and consequently change the microstructure of the ®nal product. Ó
Polymer, 2004
The purpose of this study is to develop novel poly(vinyl alcohol) (PVA)/poly(ethylene glycol) (PEG) hydrogel blends and PVA-derived organic-inorganic hybrid materials and perform nanostructural characterizations. PVA and PEG hydrogels were prepared by dissolving the polymer in aqueous solution, followed by addition of glutaraldehyde (GA) chemical crosslinker. Hybrids were synthesized by reacting PVA in aqueous solution with tetraethoxysilane (TEOS). PVA/TEOS were also modified in the nanometer-scale by crosslinking with GA during the synthesis reaction. Hydrogels and hybrids were characterized by using small-angle X-ray scattering synchrotron radiation (SAXS) and Fourier transform infrared spectroscopy (FTIR). Thin film samples were prepared for SAXS experiments. SAXS results have indicated different nano-ordered disperse phases for hydrogels made of PVA, PEG, PVA/GA, PVA/PEG. Also, PVA/TEOS and PVA/TEOS/GA hybrids have indicated different X-ray scattering patterns. FTIR spectra have showed major vibration bands associated with organicinorganic chemical groups present in the hybrid nanocomposites PVA/TEOS and PVA/TEOS/GA. PVA/PEG hydrogels and PVA-derived hybrid materials were successfully produced with GA crosslinking in nanometer-scale network. q
Poly(vinyl alcohol) Hydrogels: The Old and New Functional Materials
International Journal of Polymer Science, 2021
Hydrogels have three-dimensional network structures, high water content, good flexibility, biocompatibility, and stimulation response, which have provided a unique role in many fields such as industry, agriculture, and medical treatment. Poly(vinyl alcohol) PVA hydrogel is one of the oldest composite hydrogels. It has been extensively explored due to its chemical stability, nontoxic, good biocompatibility, biological aging resistance, high water-absorbing capacity, and easy processing. PVA-based hydrogels have been widely investigated in drug carriers, articular cartilage, wound dressings, tissue engineering, and other intelligent materials, such as self-healing and shape-memory materials, supercapacitors, sensors, and other fields. In this paper, the discovery, development, preparation, modification methods, and applications of PVA functionalized hydrogels are reviewed, and their potential applications and future research trends are also prospected.
Textural properties of silica-based organic-inorganic polymer hybrid xerogels
2000
Samples of xerogels containing organic polymers were prepared by the sol-gel method via the r eac- tion of tetraethoxysilane (TEOS) and organic monomers with an acidic catalyst. These materials were obtained as transparent and homogeneous bulk materials. The samples were characterized by Raman and IR spectroscopies, N2-adsorption (77 K), and atomic force microscopy (AFM). Specific surface areas and porosities of
Control of micro/mesoporosity in non-hydrolytic hybrid silicophosphate xerogels
J. Mater. Chem. A, 2015
Non-hydrolytic sol-gel reactions of acetoxysilanes with trimethylsilyl esters of phosphoric and phosphonic acids produce cross-linked matrices containing homogeneous dispersions of silicon and phosphoryl groups connected together by networks of Si-O-P(]O) linkages. These polycondensation reactions proceed cleanly and under mild conditions for a wide variety of precursor silanes R n Si(OAc) 4Àn (R ¼ alkyl, aryl; n ¼ 1, 2) and phosphoryl compounds RP(O)(OSiMe 3 ) 2 (R ¼ alkyl, aryl) to provide hybrid xerogels, the final properties of which are a sensitive function of the organic substituents and the Si : P ratio of the precursors. The reactions of bridged acetoxysilanes (AcO) 3 Si-X-Si(OAc) 3 and phosphoryl reagents (Me 3 SiO) 2 P(O)-X-P(O)(OSiMe 3 ) 2 have also been investigated and found to produce gels that exhibit large surface areas (up to 700 m 2 g À1 ). The presence of SiO 6 structural units in bridged-phosphoryl xerogels is related to their microporosity while the absence of such moieties in bridged-acetoxysilane networks is congruent with significant mesoporosity. Several important parameters are identified which can be used to tailor the properties of these hybrid matrices such that gels with specific polarity, porosity and surface area can be targeted at the time of synthesis.
Synthesis of hydrophilic and hydrophobic xerogels with superior properties using sodium silicate
Microporous and Mesoporous Materials, 2011
Highly porous hydrophilic and hydrophobic silica xerogels were synthesized by surface modification of silica hydrogels at ambient pressure drying. The silica hydrogels were prepared by a sol–gel polymerization of an inexpensive silica precursor (sodium silicate) under atmospheric conditions. In order to minimize shrinkage due to drying, the hydrogel surface was modified using trimethylchlorosilane (TMCS) in the presence of ethanol/n-hexane solution before ambient pressure drying (APD). Properties of the final product ...
New chemical hydrogels based on poly(vinyl alcohol)
Journal of Polymer Science Part A: Polymer Chemistry, 1996
SYNOPSIS The syntheses of two new types of chemical hydrogels based on poly(viny1 alcohol), PVA, are reported. Common to both synthetic routes is the preparation of a telechelic PVA (tel-PVA) obtained by periodate splitting of the vicinal diol units present in few percent along the chain. tel-PVA was then used as crosslinking agent with chitosan and PVA in two simple reactions in aqueous phase such as reductive alkylation of chitosan and acetalyzation of PVA. Both reactions yielded firm wall-to-wall networks showing marked differences in their swelling capability. 0 1996 John Wiley & Sons, Inc.
A Convenient Synthesis of Silylated Silica Xerogels
Chemistry of Materials
Treated silica xerogels with controlled porosity and surface area were prepared by the in situ treatment of hydrogels with hexamethyldisiloxane or alkylchlorosilanes in the presence of isopropyl alcohol. The resulting hydrogels were hydrophobic and readily transferred to nonpolar organic solvents upon contact. The surface area and porosity of the xerogel were controlled by varying the pH, time, and temperature used to polymerize the hydrogel prior to treatment. In general, the surface area decreased with increases in aging time or temperature, whereas the total pore volume and pore size increased. Silylation of the hydrogel in the aqueous phase retains the structure of the hydrogel and permits isolation with minimum structure collapse. By using this technique, silylated xerogels with surface areas ranging from 200 to >700 m 2 /g and pore volumes of 1.5 to 3.8 cm 3 /g were obtained.
Colloid Journal, 2005
The xerogels, containing phosphonic acid groups =Si(CH2)2P(0)(OC2H5)2 in the surface layer of their particles, are synthesized by the sol-gel method (ethanol as a solvent and fluoride ion as a catalyst). It is shown that, when 2 : 1, 3 : 1, and 4 : 1 aethoxysilane/(diethylphosphatoethyl)triethoxysilane ratios are used, nonporous substances are formed, at 6 : 1,8 : 1, and 10 : 1 ratios, the xerogels with highly porous structures are produced (the specific is 505-534 rn2Ig, the sorption pore volume is 0 . 3 0 . 5 3 cm3/g, and the pore diameter is 3.6-4.6 nm).
Thermal analysis of poly(dimethylsiloxane)-modified silica xerogels
Materials Letters, 2002
Organically modified silicates (ORMOSIL) have been prepared by incorporating poly(dimethylsiloxane) (PDMS) into silica xerogels, with tetraethyl orthosilicate (TEOS) as the starting inorganic material, by (i) one-step acid-or base-catalyzed process and (ii) two-step acid/base-catalyzed sol-gel process. The condensation between PDMS and TEOS have been studied to get an idea how experimental parameters control them by using thermal analysis (differential thermal analysis (DTA) and thermal gravimetric analysis (TGA)). It has been found that a base environment enhances the co-condensation between the PDMS and TEOS, whereas an acidic environment has more influence on the hydrolysis reactions. The results are reported in this communication along with possible explanations behind the observations.