Hui Dave, Nawaz Mohammed, Morris Daniel P, Edwards Martin R, Saunders Brian R
Polymer Science and Engineering Group, Manchester Materials Science Centre, School of Materials, The University of Manchester, Grosvenor Street, Manchester, M1 7HS, UK.
J Colloid Interface Sci. 2008 Aug;324(1-2):110-7. doi: 10.1016/j.jcis.2008.05.035. Epub 2008 May 27.
This work involves an investigation of pH-triggered heteroaggregation and gelation within mixed dispersions of polystyrene (PS) and pigment particles. The PS particles were stabilised by a carboxylated alkyl ethoxylate surfactant which is pH-responsive. The pigment used was beta-copper phthalocyanine. The pigment particles contained a co-surfactant system consisting of the carboxylated alkyl ethoxylate and a non-ionic surfactant. The latter was a beta-naphthol ethoxylate. The PS and pigment particles were characterised using SEM, TEM, photon correlation spectroscopy and electrophoretic mobility measurements. The PS dispersions exhibited pH-triggered aggregation when the pH was decreased to below a critical value (pH(crit)), which was 1.9. Concentrated PS dispersions formed stable particle gels at pH values less than or equal to pH(crit). Dilute pigment dispersions were found to have a pH(crit) of 3.45. However, concentrated pigment dispersions did not form gels when the pH was decreased to below pH(crit). A phase diagram for the mixed dispersions was constructed which showed a gel phase existed at pH values between 2.0 and 3.0, which corresponds to a pH region higher than pH(crit) for the PS particles. This implicates PS-pigment inter-particle bonds in the gel structure. The heteroaggregate gels were investigated using dynamic rheological measurements and it was apparent that the highest elastic modulus values were obtained in the pH range of approximately 2 to 3. SEM images provided evidence of heteroaggregates with diameters of a few micrometers. These primary heteroaggregates are suggested to be the network forming unit for the gels formed in mixed dispersions. The data from the study are used to propose a conceptual model for the structure of the heteroaggregate gels.
这项工作涉及对聚苯乙烯（PS）和颜料颗粒混合分散体系中pH触发的异质聚集和凝胶化的研究。PS颗粒由具有pH响应性的羧化烷基乙氧基化物表面活性剂稳定。使用的颜料是β-铜酞菁。颜料颗粒包含由羧化烷基乙氧基化物和非离子表面活性剂组成的共表面活性剂体系。后者是β-萘酚乙氧基化物。使用扫描电子显微镜（SEM）、透射电子显微镜（TEM）、光子相关光谱和电泳迁移率测量对PS和颜料颗粒进行了表征。当pH值降至临界值（pH(crit)）以下时，PS分散体表现出pH触发的聚集，该临界值为1.9。在pH值小于或等于pH(crit)时，浓缩的PS分散体形成稳定的颗粒凝胶。发现稀释的颜料分散体的pH(crit)为3.45。然而，当pH值降至pH(crit)以下时，浓缩的颜料分散体不会形成凝胶。构建了混合分散体的相图，该相图显示在pH值介于2.0和3.0之间存在凝胶相，这对应于高于PS颗粒pH(crit)的pH区域。这表明凝胶结构中存在PS-颜料颗粒间键。使用动态流变学测量对异质聚集凝胶进行了研究，很明显在大约2至3的pH范围内获得了最高的弹性模量值。SEM图像提供了直径为几微米的异质聚集体的证据。这些初级异质聚集体被认为是混合分散体中形成凝胶的网络形成单元。该研究的数据用于提出异质聚集凝胶结构的概念模型。
