A single-stage swelling and polymerization method was proposed for the synthesis of monodisperse porous poly(vinyl acetate-co-divinylbenzene) [poly(VAc-co-DVB)] particles with different VAc/DVB feed ratios. The particles obtained with the VAc/DVB feed ratio of 50:50 v/v had a narrow pore size distribution exhibiting a sharp peak at 30 nm. Based on this distribution the mean pore size and the specific volume were determined as 12 nm and 1.39 mL/g, respectively. The specific surface area of poly(VAc-co-DVB) particles was found to be 470 m2/g. These properties make poly(VAc-co-DVB) particles a promising support for potential HPLC applications. Poly(vinyl alcohol-co-divinylbenzene) [poly(VA-co-DVB)] particles were then obtained by the basic hydrolysis of poly(VAc-co-DVB) particles. The hydroxyl groups on poly(VA-co-DVB) particles have a suitably reactive functionality for surface grafting or derivatization protocols aiming at synthesizing various HPLC packings. The examination of poly(VA-co-DVB) particles by confocal laser scanning microscopy showed the homogeneous distribution of hydroxyl functionality in the particle interior. As a starting point, the chromatographic performance of plain material, poly(VAc-co-DVB) particles produced with VAc/DVB feed ratio of 50:50 (v/v) was tested by a commonly utilized chromatographic mode, reversed phase chromatography. Poly(VAc-co-DVB) particles were successfully used as packing material in the RP separation of alkylbenzenes with resolutions higher than 1.5. Theoretical plate numbers up to 17 500 plates/m were achieved. No significant change both in the chromatographic resolution and column efficiency was observed with increasing flow rate. The chromatography showed that poly(VAc-co-DVB) particles were a suitable starting material for the synthesis of chromatographic packings for different modes of HPLC. 相似文献
Organo-fly ash(OFA) was prepared with pretreated fly ash(FA) and hexadecyltrimethyl ammonium bromide (HDTMAB),and the composites composed of OFA and polyaniline were obtained by emulsion polymerization at different OFA weight ratios(2.0 wt%,5.0 wt%,10.0 wt%,15.0 wt%and 20.0 wt%) in the presence of dodecylbenzenesulfonic acid as dopant and emulsifier.A polymerization procedure was supposed.The electrical conductivities of the composites were tested by the four-probe technique.The chemical structure and crystallinity of the composites were confirmed by FT-IR and X-ray diffraction,respectively.Morphologies of FA,OFA and the composites were observed by SEM.The element analysis was performed by energy dispersive spectrometry.The thermal stability of the composites was analyzed by TGA.The results showed that the electrical conductivity of the composites decreased with increasing the feed weight ratio of OFA,and the lowest value was 0.62 S/cm.HDTMAB and PAn were just adsorbed on the surface of FA and OFA,respectively according to the physical adsorption without destroying the crystalline structure of FA or OFA.The surface became smoother after organification of FA by using HDTMAB,and its content on FA surfaces was about 26.9 wt%.The core/shell structure of the composite was observed by SEM analysis.The composites showed a higher thermal stability than pure PAn by introduction of OFA into this polymerization system,the heat stability of PAn was increased by decreasing 31.8 wt%of weight loss after introducing 20 wt%of OFA. 相似文献
A method of increasing the stability ofo/w emulsions and providing a potential additional barrier to drug release from the oil droplets is described. Diacryloyl derivatives of non-ionic block copolymers (poloxamers) have been used to stabilise isopropyl myristate in water emulsions. Cross-linking of these stabilisers at the oil-water interface produces a polymeric region which increases the stabilityo/w emulsions to centrifugation and of thew/o emulsions to creaming. 相似文献
The influence of succinylation on the interfacial behaviour and emulsifying properties of the main storage protein (legumin) from faba beans was studied. Results of surface tension measurements and surface shear rheometry and properties of n-decane-water emulsions indicate an increased interfacial activity by succinylation whereby the 65% succinylated legumin was the most active derivative.
The equilibrium surface pressure Πe increased from 16.6 to 20.21 mN m−1 and the critical association concentration, i.e. the subphase concentration at which the plateau of Πe was reached, strongly decreased with succinylation from 76.6 × 10−6 to 0.84 × 10−6 g ml−1. Spread and adsorbed films of legumin exhibited purely viscous behaviour under shear stress whereby the viscosity strongly increased with succinylation (from 7.93 to 93.36 μN s m−1). The droplet size of legumin-stabilized emulsions decreased and the coalescence stability increased with succinylation. The comparison with acetylated legumin supports the view that the dissociated but rather globular subunit is the most interfacially active component of acylated legumin. 相似文献
To clarify the influence of additives on the grafting phenomenon as well as the particle behavior more precisely, we carried out a model emulsion polymerization of vinyl acetate (VAc) in a 1% aqueous solution with ammonium persulfate (APS) using poly (vinyl alcohol) (PVA) as a protective colloid in the presence of additives. The addition of alcohol to the system remarkably affected the particle formation, especially grafting. This is thought to be attributed to competition between hydrogen abstraction from PVA and alcohol with a sulfate radical. Especially, the addition of acetone to the system decreased grafting to a great extent, resulting in an increase in the particle size together with an increase in the number of polymer molecules in a polymer particle. This result is thought to arise from a combination of electron abstraction from acetone with a sulfate radical and the chain-transfer reaction of the propagation radical with acetone. 相似文献
Spreading of a drop of an emulsion made with milk proteins on air/water interfaces was studied. From an unheated emulsion, all oil molecules could spread onto the air/water interface, indicating that the protein layers around the oil globules in the emulsion droplet were not coherent enough to withstand the forces involved in spreading. Heat treatment (90 °C) of emulsions made with whey protein concentrate (WPC) or skim milk powder reduced the spreadability, probably because polymerisation of whey protein at the oil/water interface increased the coherence of the protein layer. Heat treatment of emulsions made with WPC and monoglycerides did not reduce spreadability, presumably because the presence of the monoglycerides at the oil/water interface prevented a substantial increase of coherence of the protein layer. Heat treatment of caseinate-stabilised emulsions had no effect on the spreadability. If proteins were already present at the air/water interface, oil did not spread if the surface tension (γ) was <60 mN/m. We introduced a new method to measure the rate at which oil molecules spread from the oil globules in the emulsion droplet by monitoring changes in γ at various positions in a ‘trough’. The spreading rates observed for the various systems agree very well with the values predicted by the theory. Spreading from oil globules in a drop of emulsion was faster than spreading from a single oil drop, possibly due to the greater surface tension gradient between the oil globule and the air/water interface or to the increased oil surface area. Heat treatment of an emulsion made with WPC did not affect the spreading rate. The method was not suitable for measuring the spreading rate at interfaces where surface active material is already present, because changes in γ then were caused by compression of the interfacial layer rather than by the spreading oil. 相似文献