Synthesis and rheology of pH-responsive particles with shape anisotropy
type: CreativeWork
description: Seeded emulsion polymerization is used to produce large quantities of shape anisotropic, amphoteric particles in a size range of about 1 µm. Two different kinds of shape anisotropic particles are prepared for comparison to study the effects of incorporating pH-responsive groups on the properties of suspensions containing shape anisotropic colloidal particles. Copolymer dicolloids (CDC) containing pyridine groups are synthesized by swelling spherical, lightly cross linked polystyrene seeds with mixture of styrene and 2-vinyl pyridine (2VP) followed by secondary polymerization. Homopolymer dicolloids (HDC) are made in a similar procedure with only pure styrene swollen into seeds. To investigate the effects of weak attractions, the particles are coated with the nonionic surfactant hexaethylene glycol monododecyl ether (C12E6). As confirmed by electrophoretic mobility measurements as a function of pH, the CDC particles continue to show amphoteric properties. States of aggregation of dilute suspensions are mapped as functions of ionic strength and pH. The CDC particles show amphoteric behavior with strong attractions in medium pH range, while HDC remain stable at all pH’s studied (3<pH<9) unless ionic strength is increased to 5M showing that the C12E6 protects against aggregation into a primary van der Waals minimum as would be seen for bare polymer particles. The flow properties of glassy and gelled suspensions of CDC and HDC are studied as a function of volume fraction and pH. HDC particles display a high kinetic arrest volume fraction (ϕg>0.5) with small linear elastic modulus (G0’*) above ϕg at different pH conditions and ionic strengths up to 0.5M proving again that the particles experience repulsive or weakly-attractive conditions. The CDC particles behave in a similar manner at high or low pH at an ionic strength, [I] of 0.001M, but gel at a volume fraction of ϕg<0.3 and display anomalously large G0’* at the gel transition at intermediate pH or at pH=9 and I=0.5M.…
abstract: Seeded emulsion polymerization is used to produce large quantities of shape anisotropic, amphoteric particles in a size range of about 1 µm. Two different kinds of shape anisotropic particles are prepared for comparison to study the effects of incorporating pH-responsive groups on the properties of suspensions containing shape anisotropic colloidal particles. Copolymer dicolloids (CDC) containing pyridine groups are synthesized by swelling spherical, lightly cross linked polystyrene seeds with mixture of styrene and 2-vinyl pyridine (2VP) followed by secondary polymerization. Homopolymer dicolloids (HDC) are made in a similar procedure with only pure styrene swollen into seeds. To investigate the effects of weak attractions, the particles are coated with the nonionic surfactant hexaethylene glycol monododecyl ether (C12E6). As confirmed by electrophoretic mobility measurements as a function of pH, the CDC particles continue to show amphoteric properties. States of aggregation of dilute suspensions are mapped as functions of ionic strength and pH. The CDC particles show amphoteric behavior with strong attractions in medium pH range, while HDC remain stable at all pH’s studied (3<pH<9) unless ionic strength is increased to 5M showing that the C12E6 protects against aggregation into a primary van der Waals minimum as would be seen for bare polymer particles. The flow properties of glassy and gelled suspensions of CDC and HDC are studied as a function of volume fraction and pH. HDC particles display a high kinetic arrest volume fraction (ϕg>0.5) with small linear elastic modulus (G0’*) above ϕg at different pH conditions and ionic strengths up to 0.5M proving again that the particles experience repulsive or weakly-attractive conditions. The CDC particles behave in a similar manner at high or low pH at an ionic strength, [I] of 0.001M, but gel at a volume fraction of ϕg<0.3 and display anomalously large G0’* at the gel transition at intermediate pH or at pH=9 and I=0.5M.…
author: Jiang, Tianying
language: en
keywords: anisotropic particles, seeded emulsion polymerization, pH-response, multiple yielding, anisotropic interaction
date published: 2011-01-14T22:42:00Z
date modified: 2026-07-22T22:25:11Z
provider: University of Illinois - Urbana-Champaign
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Illinois at Urbana-Champaign

PropertyValue
property ID: Handle
value: http://hdl.handle.net/2142/18261