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Instruments / Technical Area	Publication Details	Published	Actions
I22-Small angle scattering & Diffraction	Charging poly(methyl methacrylate) latexes in nonpolar solvents: Effect of particle concentration Gregory N. Smith , Silvia Ahualli , Angel V. Delgado , David A. J. Gillespie , Roger Kemp , Jocelyn Peach , Jonathan C. Pegg , Sarah Rogers , Olga Shebanova , Nathan Smith , Julian Eastoe Langmuir DOI: 10.1021/acs.langmuir.7b02257 Diamond Proposal Number(s): [9753] Show Abstract ▼ Abstract: The electrophoresis of a well-established model system of charged colloids in nonpolar solvents has been studied as a function of particle volume fraction at constant surfactant concentration. Dispersions of poly(12-hydroxystearic acid)-stabilized poly(methyl methacrylate) (PMMA) latexes in dodecane were prepared with added Aerosol OT surfactant as the charging agent. The electrophoretic mobility (µ) of the PMMA latexes is found to decrease with particle concentration. The particles are charged by a small molecule charging agent (AOT) at finite concentration, and this makes the origin of this decrease in µ unclear. There are two suggested explanations. The decrease could either be due to the reservoir of available surfactant being exhausted at high particle concentrations or the interactions between the charged particles at high particle number concentrations. Contrast-variation small-angle neutron scattering measurements of PMMA latexes and deuterated AOT-d34 surfactant in latex core contrast-matched solvent were used to study the former, and electrokinetic modeling were used to study the latter. As the same amount of AOT-d34 is found to be incorporated with the latexes at all volume fractions, the solvodynamic and electrical interactions between particles are determined to be the explanation for the decrease in mobility. These measurements show that, for small latexes, there are interactions between the charged particles at all accessible particle volume fractions and that it is necessary to account for this to accurately determine the electrokinetic ζ potential.	Oct 2017
I22-Small angle scattering & Diffraction	The internal structure of poly(methyl methacrylate) latexes in nonpolar solvents Gregory N. Smith , Samuel D. Finlayson , David Gillespie , Jocelyn Peach , Jonathan Pegg , Sarah Rogers , Olga Shebanova , Ann Terry , Steven P. Armes , Paul Bartlett , Julian Eastoe Journal Of Colloid And Interface Science 479, 234 - 243 DOI: 10.1016/j.jcis.2016.06.027 Show Abstract ▼ Abstract: Hypothesis Poly(methyl methacrylate) (PMMA) latexes in nonpolar solvents are an excellent model system to understand phenomena in low dielectric media, and understanding their internal structure is critical to characterizing their performance in both fundamental studies of colloidal interactions and in potential industrial applications. Both the PMMA cores and the poly(12-hydroxystearic acid) (PHSA) shells of the latexes are known to be penetrable by solvent and small molecules, but the relevance of this for the properties of these particles is unknown. Experiments These particles can be prepared in a broad range of sizes, and two PMMA latexes dispersed in n-dodecane (76 and 685 nm in diameter) were studied using techniques appropriate to their size. Small-angle scattering (using both neutrons and X-rays) was used to study the small latexes, and analytical centrifugation was used to study the large latexes. These studies enabled the calculation of the core densities and the amount of solvent in the stabilizer shells for both latexes. Both have consequences on interpreting measurements using these latexes. Findings The PHSA shells are highly solvated (∼85% solvent by volume), as expected for effective steric stabilizers. However, the PHSA chains do contribute to the intensity of neutron scattering measurements on concentrated dispersions and cannot be ignored. The PMMA cores have a slightly lower density than PMMA homopolymer, which shows that only a small free volume is required to allow small molecules to penetrate into the cores. Interestingly, the observations are essentially the same, regardless of the size of the particle; these are general features of these polymer latexes. Despite the latexes being used as a model physical system, the internal chemical structure is complex and must be fully considered when characterizing them.	Oct 2016

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