Improved volatile cargo retention and mechanical properties of capsules via sediment-free in situ polymerization with cross-linked poly(vinyl alcohol) as an emulsifier

Research output: Contribution to journalArticle

Authors

  • Abdullah Mustapha
  • Xiaotong Zhang
  • Dan Baiocco
  • Gilmore Wellio
  • Thomas Davies

Colleges, School and Institutes

External organisations

  • Cardiff Univ

Abstract


Hypothesis

It is hypothesized that poly(vinyl alcohol) (PVOH) as an emulsifier destabilizes the insoluble molecular aggregates by increasing interparticle interactions and their tendency toward agglomeration into large particle aggregates during the encapsulation process of one-step in situ polymerization. Porosity of capsule shells is expected to decrease with reducing agglomeration tendency to allow dense packing of smaller insoluble aggregates. Cross-linking the polymer network further reduces shell permeability to improve the retention of volatile cargos. PVOH also modifies the short-range order of polymer network to bestow improved mechanical properties in addition to the shell thickening effect at appropriate synthesis conditions.


Experiments

PVOH was used to stabilize a heptane-in-water emulsion as a template for producing capsules via one-step in situ polymerization. Shell morphologies at different PVOH concentrations were compared. Physical freeze-thawing and chemical cross-linking were adopted separately to synthesize capsules with a volatile cargo, and its retention was characterized qualitatively by a solvatochromism-based fluorescent method and quantitative payload calculation. Mechanical properties of capsules were tested with micromanipulation. The effect of graphene oxide (GO) impregnation into capsules was studied with various co-emulsifiers.


Findings

When PVOH alone was used as the emulsifier for capsule synthesis, the higher its concentration, the more porous the shell structure was. At very low concentrations, visible pores were eliminated. Freeze-thaw cycles reduced the permeability of capsule shells when visible pores were absent. Chemical cross-linking with poly(acrylic acid) (PAA) significantly improved the retention of volatile cargo heptane. PVOH substantially reduced polymer sediment during capsule synthesis, which eliminated the tedious centrifugation procedure that normally would have followed. Superior mechanical strength of capsules was achieved with PAA cross-linked PVOH at appropriate conditions. The impregnation of aqueously dispersed GO into capsules was also promoted by using PVOH but not hydrocolloid emulsifiers.

Details

Original languageEnglish
Pages (from-to)155-164
Number of pages10
JournalJournal of Colloid and Interface Science
Volume568
Early online date29 Jan 2020
Publication statusPublished - May 2020

Keywords

  • capsule, emulsifier, graphene oxide, poly(vinyl alcohol), sediment, volatile