Ductile polymer coatings were investigated in terms of their response to uniaxial deformation and contact deformation with respect to indentation and scratching. The effects of pigmentation, contact geometry, load and speed on the mechanical response were studied. The materials have been tested with extended spherical contacts deep into the coating layer and concentrated conical contacts close to the surface. The residual deformation pattern was examined with optical microscopy, white-light interferometry and atomic force microscopy. In the case of extended spherical contacts, corresponding to small effective strains, there was a correlation between the magnitude of residual deformation and the tensile strength. In the case of concentrated conical contacts, corresponding to larger strains, the materials were ranked differently. Reproducible failure transitions were detected with increased scratch load for the conical contacts. These failure transitions could not be directly linked to uniaxial break parameters. Stratification appears to be an issue in pigmented coatings. The effect of pigmentation was increased tensile stiffness and improved scratch resistance.

The viscoelasticity of two thermally crosslinked polymer coatings was examined in terms of relaxation of the applied stress after a sudden strain. Two different transient methods were utilized: flat-ended cylindrical indentation testing of polymer film on a rigid substrate and tensile testing of a corresponding free-standing polymer film. The correlation between tensile and indentation tests was studied. The mechanical response of a viscoelastic layer deposited on a rigid substrate was investigated as a function of indentation depth. there was good agreement between the results of the tensile and indentation tests for thick film layers at moderate indentation depths. The findings indicate that the substrate influences the coating performance by reducing the viscous contribution to the stress response hand amplifying the magnitude of the equilibrium modulus for large indentation depths. The indentation method utilized here was shown to be a potentially suitable tool for the determination of Poisson's ratio of polymer films.

The scope of this work has been to investigate storage and recovery processes in ductile polymer coatings. The effects of storage have been measured in terms of variations in mechanical response with time. The use of contact tests in combination with sophisticated surface imaging tools offered unique possibilities to monitor deformation recovery over long periods of time. The kinetics of the recovery processes has been monitored. Polyurethane coatings were found to recover in a similar fashion to a viscous liquid. By comparing the time scale of the recovery with transient tests, it was evident that this was not a viscoelastic effect. The effect of exposure to water and humidity on deformation response and recovery was significant for polyurethane coatings. In addition, high amounts of pigmentation had a great effect on recovery processes. Surface-, bulk-, and interfacial-properties were greatly affected by storage time.

Two ductile coating ma-terials were subjected to a combined indentation and scratch test procedure de-signed to screen a predetermined pattern of many small sample surfaces in a limited time. The screening of 50 surface spots ordered in a matrix pattern on the surface was carried out in 4.5 hr. The test provides reproducible data in terms of indentation modulus, elastic recovery, scratch penetration depth, and scratch residual depth, and also offers the possibility of detecting critical mechanical transitions such as rupture. The presented procedure produces sufficient data in a limited time scale to fulfill the requirements for a fast method to screen coating compositions.

The use and interpretation of contact scratch tests on polymer coatings has been investigated. The influences from test parameters such as scratch speed, contact geometry and load on the deformation response were examined. Two ductile polymer coatings of commercial grade tailored for pre-painted steel applications were used as model systems. The residual deformation pattern was examined with optical microscopy, white-light interferometry, and atomic force microscopy. Free-standing coating films were also subjected to static, transient and dynamic tensile testing to find a correlation between the intrinsic coating properties and the scratch behavior. The results indicate that the use of a single set of contact parameters is insufficient to reflect the overall response of a coating material to real contact conditions. A well-designed scratch test will however give a substantial amount of useful information.

Dielectric permittivity and loss have been measured over the frequency range 0.1–1000 Hz between 80 K and 300 K for side-chain and network liquid crystalline polyacrylates obtained by photopolymerization of smectic monomers. The polyacrylates were based on mixtures of chiral monofunctional monomers with a lateral nitro group attached to the outer phenyl group of the mesogen and an ester group in the mesogen and nonchiral bifunctional monomers, either with an ester group in the mesogen or with an ester group in the mesogen and a lateral nitro group, creating networks with different crosslink densities. Poled copolymers based on these monomers exhibit second-order nonlinear optical properties. Polymers based only on monomers with the chiral and nitro groups exhibited a pronounced γ process, associated with segmental motions in the methylene spacer groups and only vague signs of the high-temperature subglass process (β) associated with reorientation of the mesogen. The polymers with the bifunctional monomer without the nitro group exhibited clearly both γ and β processes. The dielectric data indicate that the ester groups in the bifunctional units undergo conventional reorientation according to the β mechanism and that the β process is suppressed in the pendant chains with the lateral nitro groups. The β process involves a coordinated torsion about two bonds in the mesogen and the swept-out volume involved in the motion becomes extensive when a lateral nitro group is present. © 1997 Elsevier Science Ltd.