Polystyrene plastic deformation

The relationship between the increase in contact radius due to plastic deformation and the corresponding increase in the force required to detach submicrometer polystyrene latex particles from a silicon substrate was determined by Krishnan et al. [108]. In that study, Krishnan measured the increase in the contact area of the partieles over a period of time (Fig. 7a) and the corresponding decrease in the percentage of particles that could be removed using a force that was sufficient to remove virtually all the particles initially (Fig. 7b). 

Many examples in the literature show that plastic deformation even of glassy polymers, such as polystyrene, may occur under relatively modest loads in CM-AFM experiments. As summarized in Fig. 3.16. the formation of more or less regularly spaced ridges perpendicular to the fast scan direction is observed. The amplitude of the ridges increases over time (from top to bottom in Fig. 3.16a) and... 

Polystyrene and other materials have been reported to be plastically deformed at temperature even below Tg (compare, e.g., Sect. 3.2 in Chap. 3) thus, such experiments are most likely carried out beyond the elastic contact limit and surface damage may prevail. 

C). This picture could resemble a plastic deformation of the bead of linear polystyrene. However, the residual deformation of the hypercrosslinked network cannot be regarded as plastic. 

After the introduction of polar sulfonic functions or quaternary ammonium groups into the polystyrene network, the material becomes hydro-phihc water solvates the polar groups of the polymer chains, thus plasticizing the polymeric phase. As in the case of removing toluene from nonpolar sorbents by drying, the removal of water from the hydrophilic matrices of ion-exchange resins is accompanied mainly by non-elastic, plastic, deformations of the polymer network stressed by capillary contraction. Under these conditions of plasticization of the polymer phase by water, the desweUing anomaly manifests itself primarily as an abrupt decrease in the bead volume, with a subsequent slow approach to an... 

Scanning electron microscope studies were performed on polystyrene spheres sitting on polished silicon surfaces by Rimai, Demejo and Bowen. The bulk polymer had a Young s modulus of 2.55 GPa and a yield stress of 10.8 MPa when measured on a testing machine. With such a low yield point it was estimated that the particles should be plastically deformed under the adhesion forces. Therefore they applied the plastic deformation theory of Maugis and Pollock to fit the results, as shown in Fig. 9.28. This gave the expression for contact diameter d in terms of sphere diameter D... 

The solvent-etched specimen was first polished. The spherical holes indicate the presence of spherical polystyrene particles (Fig. 11.17(a)). The fracture surface contains many small spherical particles which consist of polystyrene. The polyethylene component had undergone some plastic deformation which is seen in the microfibrils appearing in the micrograph (Fig. 11.17(b)). 

Zafeiropoulos N E, Davies R J, Schneider K, Burghammer M, Riekel Ch and Stamm M (2006) The relationship between craze structure and molecular weight in polystyrene as revealed by SAXS experiments, Macromol Rapid Commun 27 1689-1694. Galeski A, Argon A S and Cohen R E (1988) Changes in the morphology of bulk spherulitic nylon 6 due to plastic deformation, Macromolecules 21 2761-2770. 

Kojinia Y, Usuki A, Kawasumi M, Okada A, Fukushima Y, Kurauchi T and Kaniiga-ito O (1993) Mechanical properties of nylon 6-clay hybrid, J Muter 8 1185-1189. Aoike T, Uehara H, Yamanobe T and Komoto T (2001) Comparison of macro- and nanotribological behavior with surface plastic deformation of polystyrene, Langmuir 17 2153-2159. 

Freeze fracture has been used to study the structure of colloidal particles in water-oil mixtures stabilized by polymer emulsifiers. Microemulsions consisting of water, toluene, and graft copolymer composed of a polystyrene backbone and a PEO graft were deposited onto a small gold plate, quenched in liquid nitrogen in equilibrium with its own solid phase [582]. Replicas of the fractured surfaces were washed with tetra-hydrofuran, which showed the micellar structure of the copolymers. Classical microemulsions have been studied [583], and micellar aggregates of copolymers have been shown [584, 585]. Polymer latexes have been prepared using simUar methods by Sle)rtr and Robards [586]. The emphasis in this review was on the plastic deformation observed in the fi eeze fracture method and in ultrathin frozen sections. 

The incorporation of rubber particles into a brittle polymer has a profound effect upon the mechanical properties as shown from the stress-strain curves in Fig. 5.66. This can be seen in Fig. 5.66(a) for high-impact polystyrene (HIPS) which is a blend of polystyrene and polybutadiene. The stress-strain curve for polystyrene shows brittle behaviour, whereas the inclusion of the rubbery phase causes the material to undergo yield and the sample to deform plastically to about 40% strain before eventually fracturing. The plastic deformation is accompanied by stress-whitening whereby the necked region becomes white in appearance during deformation. As will be explained later, this is due to the formation of a large number of crazes around the rubber particles in the material. 

Creep. The creep characteristic of plastic foams must be considered when they are used in stmctural appHcations. Creep is the change in dimensions of a material when it is maintained under a constant stress. Data on the deformation of polystyrene foam under various static loads have been compiled (158). There are two types of creep in this material short-term and long-term. Short-term creep exists in foams at all stress levels however, a threshold stress level exists below which there is no detectable long-term creep. The minimum load required to cause long-term creep in molded polystyrene foam varies with density ranging from 50 kPa (7.3 psi) for foam density 16 kg/m (1 lb /ft ) to 455 kPa (66 psi) at foam density 160 kg/m (10... 

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