Yung-Wei Yang

Crystal thicknesses in semicrystalline oxyethylene/oxybutylene block copolymers by atomic force microscopy and SAXS

Abstract The structure of thin crystallized films of a diblock or a triblock copolymer deposited on silicon has been investigated using atomic force microscopy (AFM). Non-contact mode AFM was used to investigate the topography of crystallites of poly(oxyethylene)/poly(oxybutylene) (E/B) block copolymers at room temperature, where E is crystallized and B is amorphous. The crystal thicknesses determined from AFM were compared to bulk layer spacings determined using small-angle X-ray scattering (SAXS). This technique showed that E 41 B 22 E 41 (the subscript denotes the number of repeat units) largely crystallized in a monolayer with unfolded E blocks at the substrate and folded (looped) B blocks at the polymer-air interface, and with the E blocks tilted at an angle of ca. 60° relative to the substrate plane. Multiple layers with a common step height were observed for the diblock E 27 B 6 crystallites, which were largely comprised of unfolded chains, also with E block tilted at an angle of ca 60° with respect to the substrate plane.

Cooperative association of diblock and triblock copolymers in aqueous solution. A study of mixed micelles of block-copoly(oxyethylene/oxybutylene) and block-copoly(oxybutylene/oxyethylene/oxybutylene)

Block copolymers of ethylene oxide and 1,2-epoxybutane, B8E41 and B12E76B12, have been synthesized and purified, and their association properties in aqueous solution studied by surface tension and static and dynamic light scattering. A 50 : 50 wt.% mixture of the two copolymers in dilute aqueous solution formed mixed micelles in which the triblock copolymer molecules were predominantly in the looped conformation. At higher concentrations (e.g. 100 g dm–3) the mixed micelles themselves associated to form micellar clusters which were bridged by triblock copolymers in the extended conformation. The results include micelle and cluster association numbers.

Mixed micelles of block copolymers of ethylene oxide and 1,2-butylene oxide. Solutions and gels of triblock BEB plus diblock EB copolymers studied by light scattering and rheology

Because of the hydrophobic end blocks, micelles of triblock BEB copolymers (E denotes an oxyethylene unit, B an oxybutylene unit) formed in aqueous solution show effects attributable to intermicellar bridging. The formation of mixed micelles with a diblock EB copolymer reduces but does not eliminate the effect. Light scattering methods applied to dilute solutions have been used to show that this is the case for mixed micelles of B12E114B12 and E43B11 (the subscripts denote block lengths). This work focuses on 20 wt% aqueous solutions and on the effect of mixing on properties relating to the gel state, i.e. dynamic storage modulus (G′) and yield strength (σy). There are two contributory factors determining the gel properties: micelle bridging and micelle packing, with just the latter operative for a diblock gel. Increasing the proportion of diblock copolymer in the mixture reduces the contribution from micelle bridging. Considering 20 wt% solutions at 5 °C, the diblock copolymer solution does not gel at this temperature and values of G′ and σy fall away monotonically to zero. For 20 wt% solutions at 25 °C, the diblock copolymer solution does gel at this temperature and values of G′ and σy pass through minima as the system is changed from 100% triblock to 100% diblock copolymer.

Aqueous micellar solutions of a triblock copolymer of ethylene oxide and 1,2-butylene oxide, B12E114B12. Scaling the viscoelasticity of fluid and gel

Aqueous solutions of triblock copolymer B12E114B12 have been characterised rheometrically over the concentration range 10–40 wt.% and at several temperatures. Through micellar bridging the micellar interaction is weakly attractive. A wide variety of linear viscoelastic behaviours are observed, and it is shown that they can be superposed onto a master curve of the type developed by Trappe and Weitz (Phys. Rev. Lett., 2000, 85, 449) for conventional colloidal suspensions of weakly-attractive particles.

Association and phase behaviour of statistical and block copolymers of ethylene oxide and butylene oxide in water

Three copolymers of ethylene oxide (EO) and 1,2-butylene oxide (BO) were prepared by anionic polymerization to have similiar molar masses (Mn ≈ 7000 g mol-1), molar mass distributions (Mw/Mn

Gelation of aqueous solutions of diblock and triblock copolymers of ethylene oxide and 1,2-butylene oxide studied by 1H nuclear magnetic relaxation

1 H NMR longitudinal and transverse relaxation times have been measured as a function of temperature at 300 and 500 MHz for aqueous solutions of diblock and triblock copolymers of ethylene oxide (E) and 1,2-butylene oxide (B), encompassing micellar sol and gel phases. At the phase transitions from a micelle to a gel structure, transitions were observed in the relaxation times of the E block, consistent with gel formation by close packing of micelles at a spacing determined by the thermodynamic radius rather than the hydrodynamic radius. Transient nuclear Overhauser effects indicated that in the micelles there was considerable interpenetration of the E and B blocks at the core/fringe boundary. The relaxation times were analysed using a two-step correlation function. For the E block, the fast correlation time representing local segmental motions was little affected by gelation, whereas the slow correlation time representing larger-scale motions was much more affected. Towards the lowest temperatures studied (< 10 °C), the relaxation times of the B block indicated incipient micelle dissociation.

Polymer bristles: a SANS study

We report the results of a SANS study into the structure of the adsorbed layers formed at the interface in a dilute perfluorodecalinin-water emulsion by five short chain diblock copolymers of oxyethylene (OE) and oxybutylene (OB). The results are discussed in the context of the Marques-Joanny-Leibler scaling description of block copolymer adsorption from selective solvents. The volume fraction profiles are best described by parabolic and, to a lesser extent, Gaussian functional forms. On increasing the temperature the buoy segments of one copolymer were found to contract toward the surface, giving rise to profiles that were more block-like in accordance with the mean-field predictions of Wijmans and Zhulina.