The objective of the consortium is to develop and refine novel surface mechanical measurement and scratch testing methodologies of durability performance to the coating and plastics industry and its customers utilizing indentation, chemical spectroscopy, and optical scattering techniques. This includes nanocomposites, toughened thermoplastics, and multifunctional coatings.
High-performance coatings and plastics are an important and expensive component of building and infrastructure sustainability. The increasing use of these materials is not just for new building construction and but also for repair and replacement of building and infrastructure to enhance performance and reliability, thus improving safety. For example: if the substrate is exposed by coating failure, corrosion and degradation will occur and the outcome potentially leads to significant damage to the building envelope. Even superficially damaged coatings may require expensive repair because consumers perceive the coating as failed and further assume building is unsafe. An important strategy for preventing these failures is to design coatings that resist mechanical damage. These systems, such as nanocomposites, particle-filled materials, coatings on plastics and metals, multifunctional and hybrid polymer coatings, are often made of multi-layers, multi-components. Thus, surface and interface/ interphase play a major role on the durability performance of sustainable physical infrastructure materials. However, measurement science is lacking for characterizing surface and interface/interphase of multi-layer, multi-component polymeric systems, especially in area of (1) accurate, spatially resolved measurements of mechanical properties at the nanometer level in the surface and interface regions, (2) in-situ hardness and modulus measurements during the curing process, (3) a robust quantitative measure of the coating scratch resistance, and (4) a methodology for linking surface and interface mechanical properties to scratch resistance for evaluating the durability performance properties.
Recognizing the complexity and importance of the interface/interphase (including film/air interface) on the performance and service life of polymeric systems, NIST and Visteon held numerous meetings and sponsored two workshops in 1997 and 1999 to address the problems on "Characterization and Modeling of the Interface/Interphase of Polymeric Materials and Systems". As a result of these workshops and further discussion with industry, an Industry/Government Consortium called "Polymer Interphase Consortium" (PIC) was officially formed in December, 2000; PIC became effective on January 18, 2001.
The main objective of PIC is to develop methodologies and metrologies for testing, characterization, and modeling of surface and interphase of polymeric coatings and plastics. There were three projects in Phase I (January 2001 – September 2004) of PIC Consortium: (1) Mechanical Characterization of Polymer Surfaces, (2) Effects of Shear Flow and Thermal Gradients, and (3) Interphase Characterization. Three projects were carefully chosen for the first phase study of the consortium to address the immediate research needs identified by the industry. In Phase I, NIST-PIC Consortium members consisted of three NIST laboratories( Building and Fire Research, Chemical Science and Technology, and Materials Science and Engineering), and four industrial partners (Visteon, Dow, PPG, and MTS) from the plastics, paint and automotive parts sectors as well as instrument manufacturers- see technical program and overview of PIC Phase I for more details.
PIC Phase II started October 1, 2004; NIST-PIC Consortium members consisted of two NIST laboratories (Building and Fire Research, and Chemical Science and Technology) and six industrial members (Visteon, DOW, PPG, MTS, Arkema, Eastman). There are three projects in Phase II: (1) Methodologies for scratch testing and relating scratch morphology to appearance properties of polymeric coatings and plastics, (2) Surface nanomechanical characterization of polymeric coatings and plastics through instrumented indentation, and (3) Application and development of photon-based imaging techniques for characterization of the chemical and morphological microstructure of polymeric materials and interfaces. Materials of interest for Phase II have included automotive clear coat systems, impact modified thermoplastics, and polymer blend architectural coatings.
Phase II was completed on March 31, 2008, and Phase III, renamed as PSI (Polymer Surface/Interface) started on January 1, 2009. Prior to the starting of Phase III, a NIST/PIC Workshop was held on January 16, 2008. We have shaped and refined our research plans to develop new methods for chemical, optical, and mechanical characterization of polymer interfaces, based on discussions and inputs from interested industrial partners on areas of interest in the field of polymer surfaces, interfaces, and interphases from the workshop. In particular, we are interested in combining these technologies to relate material properties to performance. In Phase III, there are two NIST Laboratories: Engineering Laboratory (EL) and Materials Measurement Laboratory (MML) and five PSI members are Eastman Chemical, BYK-USA, IAC North America, CSM instrument, and Boeing Co. The new focus projects are (1) Mechanical properties and failure at the surface and interface of polymeric coatings and nanocomposites; and (2) Develop methodologies for characterizing optical properties and scratch resistance assessment for polymeric coatings, plastics, and nanocomposites.
The Phase IV of PSI consortium started on May 1, 2012 . Consortium members include Eastman Chemical, BYK-USA, CSM instrument, The Boeing Co, and NIST Engineering Laboratory (EL). The focus of the research is to develop measurement science for characterizing surface damage and interfacial adhesion of polymeric coatings and composites. Major tasks include: (1). Quantitatively characterizing material multi-scale structure and properties as a function of nanofiller type, degree of dispersion, and interfacial properties; (2) Continue developing/modifying experimental techniques and procedures for measuring surface/interface properties, (3). Develop test methods/protocols to use scratch test or other methods to measure adhesion (interfacial) properties of polymeric coatings and composites.
The Phase V of PSI consortium started on September 1, 2015. Consortium members include Eastman Chemical, Anton Paar, The Boeing Co, Dow Chemical, SASIC, and NIST Engineering Laboratory (EL). The research focus of the Phase is (1) to facilitate industrial collaborations with NIST to establish weathering correlations on industrially relevant polymer chemistries and outdoor exposure sites in conjunction with SPHERE exposure experiments; (2) to develop methodologies for accelerated weathering/aging studies to better understand the mechanisms of degradation in coatings, plastics and composites in less time; (3) to develop non-invasive methods to monitor the changes in surface/interface properties (surface texture, optical, mechanical, and chemical properties) under environmental stresses (UV radiation, thermal, moisture, mechanical stresses).
Recent outputs and outcomes include:
- PSI-related publications
- New knowledge and methods to measure time-dependence of scratch behavior in complex polymer systems, including optical measurements to improve assessment of polymer relaxation immediately after scratching.
- Recommendations for selection of proper parameters to assess scratch resistance.
- Test methods, approved to consortium members, provided to industrial partners to characterize surface mechanical and scratch resistance in a multi-layer coatings as a function of curing time.
- New knowledge for characterizing optical properties of scratched multi-component of thermal plastics composites and relating surface roughness and subsurface microstructure to the visibility of a scratch under different illumination conditions and scattering configurations.
- Participated in revision of ASTM D7187 "Measuring Mechanistic Aspects of Scratch/Mar Behavior of Paint Coatings by Nanoscratching"; discussion with D1 committee to improve the test method and add PSI-developed optical scattering protocol to the existing standard.
- Drafted a measurement protocol/methodology to link surface damage to optical diffuse scattering –working with consortium industrial members to develop a standardized nanoindenter scratch test methodology to predict optical performance after field scratch tests for multi-layer composites.
- New knowledge and methods for characterizing the mechanical properties of the interface between epoxy and thin solgel films (less than 0.5 microns thick) using a novel nanoindenter test methodology.