22 research outputs found
Temperature-dependent structure and dynamics of highly-branched poly(N-isopropylacrylamide) in aqueous solution
Small-angle neutron scattering (SANS) and neutron spin-echo (NSE) have been used to investigate the temperature-dependent solution behaviour of highly-branched poly(N-isopropylacrylamide) (HB-PNIPAM). SANS experiments have shown that water is a good solvent for both HB-PNIPAM and a linear PNIPAM control at low temperatures where the small angle scattering is described by a single correlation length model. Increasing the temperature leads to a gradual collapse of HB-PNIPAM until above the lower critical solution temperature (LCST), at which point aggregation occurs, forming disperse spherical particles of up to 60 nm in diameter, independent of the degree of branching. However, SANS from linear PNIPAM above the LCST is described by a model that combines particulate structure and a contribution from solvated chains. NSE was used to study the internal and translational solution dynamics of HB-PNIPAM chains below the LCST. Internal HB-PNIPAM dynamics is described well by the Rouse model for non-entangled chains
Highly-ordered onion micelles made from amphiphilic highly-branched copolymers
Uniform onion micelles formed from up to ten nano-structured polymer layers were produced by the aqueous self-assembly of highly-branched copolymers. Highly-branched poly(alkyl methacrylate)s were chain extended with poly(acrylic acid) in a two-step reversible addition–fragmentation chain transfer-self-condensing vinyl polymerization (RAFT-SCVP) in solution. The resulting polymers were dispersed into water from oxolane (THF) using a self-organized precipitation-like method and the self-assembled particles were studied by phase-analysis light scattering, small-angle neutron scattering, and electron microscopy techniques. The relative hydrophobicity of the blocks was varied by changing the alkyl methacrylate (methyl, butyl, or lauryl) and this was found to affect the morphology of the particles. Only the poly(butyl methacrylate)-containing macromolecule formed an onion micelle structure. The formation of this morphology was observed to depend on: the evaporation of the good solvent (THF) during the self-assembly process causing kinetic trapping of structures; the pH of the aqueous phase; and also on the ratio of hydrophobic to hydrophilic segments within the copolymer. The lamellar structure could be removed by annealing the dispersion above the glass transition temperature of the poly(butyl methacrylate). To exemplify how these onion micelles can be used to encapsulate and release an active compound, a dye, rhodamine B (Rh B), was encapsulated and released. The release behaviour was dependent on the morphology of the particles. Particles formed containing the poly(methyl methacrylate) or poly(lauryl methacrylate) core did not form onions and although these materials absorbed Rh B, it was continuously released at room temperature. On the other hand, the lamellar structure formed from branch-poly(butyl methacrylate)-[poly(butyl methacrylate)-block-poly(acrylic acid)] allowed for encapsulation of approximately 45% of the dye, without release, until heating disrupted the lamellar structure
Selective Exposure to Berita Harian Online and Utusan Malaysia Online: The Roles of Surveillance Motivation, Website Usability and Website Attractiveness
News media allows audiences to be selective in determining both their news sources
and type of news stories they read. This study examined factors influencing selective
exposure to the online editions of two mainstream Malaysian newspapers, Berita
Harian and Utusan Malaysia. Using selective exposure theory as the theoretical
lens, this study compared both newspapers in terms of their audiences’ level of
surveillance motivation, and how audiences rate the newspapers’ websites with respect
to usability and attractiveness. This study used a within-subject experimental research
design that exposed 51 subjects to both Berita Harian and Utusan Malaysia online
newspapers. The results of the experiment indicate that Berita Harian and Utusan
Malaysia online were significantly different in terms of website usability; however,
no significant differences were found in terms of surveillance motivation or website
attractiveness between the two newspapers. Further analysis indicate that the only
significant predictor of selective exposure was website usability. This study highlights
the importance of website usability for online newspapers wanting to harness audience
selectivity
Poverty in Australia A study of the implications of education, household formation and the labour market experience of the young
SIGLEAvailable from British Library Document Supply Centre- DSC:3597.9342(91/10) / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Some implications of occupational segregation for Australian women
SIGLEGBUnited Kingdo
Sex discrimination and occupational segregation in the Australian labour market
This paper explores the implications of the difference between the occupational distribution for males and females in a joint model determining earnings and occupation. The male/female wage differential is evaluated for a number of broad occupational classifications. This is followed by an evaluation of the role and relative importance of inter-occupational and intra-occupational effects as contributors to the overall male/female wage differential The main conclusion following from the econometric results is that intra-occupational effects dominate Thus, policies which attempt to address the gender wage differential by re-allocation of labour across occupations are unlikely to solve the problem