PS-HEMA latex fractionation by sedimentation and colloidal crystallization

André H Cardoso,Carlos A.P Leite,Fernando Galembeck

doi:10.1590/s0103-50531999000600013

Abstract

A poly(styrene-co-hydroxyethylmethacrylate) latex underwent sedimentation under gravity followed by an spontaneous and extensive colloidal crystallization. It was then fractionated in three visually distinguishable layers. Latex aliquots layers were sampled at different heigths and the particles were characterized by PCS, microelectrophoresis, infrared spectra and analytical electron microscopy. The major fraction was opalescent and contained the colloidal crystals settled in the bottom of the liquid. Two other latex fractions were obtained, which differed in their chemical compositions, particle sizes and topochemical features from the self-arraying particles. Macrocrystallization of the fractionated latex yielded high quality crystals with a low frequency of defects, which confirms that particle chemical homogeneity is an important factor for particle self-arraying.

Highlights

Self-organized latex particle arrays[1,2], either macrocrystals or colloidal crystals, are often observed in latexes, and they have attracted the attention of many researchers
We report on the fractionation of PSHEMA latex, and we show that this leads to high-quality macrocrystal formation
Ca. 200 mL of the latex dispersion were stored in a 250-mL glass vial with a screw-cap

Summary

Introduction

Self-organized latex particle arrays[1,2], either (dry) macrocrystals or (liquid) colloidal crystals, are often observed in latexes, and they have attracted the attention of many researchers. Which the particle polidispersity as well as the presence of salt in the initial dispersion does not preclude macrocrystallization[14] In another recent work, we have obtained microchemical information on this latex, by energy-loss imaging (ESI)[15]. We have obtained microchemical information on this latex, by energy-loss imaging (ESI)[15] This showed that negative charges are distributed throughout the dry latex particles, while the positive charges make a particle shell in the dry particles, imparting to each particle a multipolar charge distribution which is relevant for particle-particle interaction and self-arraying. The latex fractions were centrifuged, the latex was dried and dissolved in toluene, to obtain the casting solutions

Results

Discussion

Conclusion