Homogeneous nanocellular foams from styrenic-acrylic polymer blends
- PDF / 882,505 Bytes
- 15 Pages / 584.957 x 782.986 pts Page_size
- 71 Downloads / 175 Views
Hyun K. Jeon The Dow Chemical Company, Dow Electronic Materials, Dow Seoul Technology Center, Hwaseong-si, Gyeonggi-do, 445-170 (Korea) (Received 12 February 2013; accepted 2 April 2013)
Nano-cellular foams were successfully produced from blends of styrenic and acrylic polymers by a two-step batch foaming process using carbon dioxide as the blowing agent. Addition of poly (ethyl methacrylate) or poly(methyl methacrylate-co-ethyl acrylate) to styrene-acrylonitrile copolymers, even at a low level, resulted in very homogeneous foams with smaller cell size and narrower cell size distribution than with the individual polymers. The best nanofoams produced from miscible blends have average cell sizes below 100 nm, cell densities up to 5 1015 cm3 and medium-to-low relative densities (void fraction between 60 and 70%). Contrary to previous studies, it was found that blends with lower CO2 solubility gave higher cell density nanofoams. This suggests new mechanisms for the nucleation of foams from these blends at the nanoscale.
I. INTRODUCTION
The production of nanoporous polymer structures is a very active area of research because of the promise of unique combinations of properties not achievable with microcellular or macrocellular foams. Films and membranes with connected nanopores are used as catalyst support due to their high surface area, or as filtration or separation media in which the balance of properties such as particle rejection and flux can be tuned by adjusting the pores size distribution. Nanoporous membranes also find their application as battery separators, in the transport of ions, and can be controlled by hindered diffusion in the narrow channels. Other potential applications of these high surface area materials include biosensors, scaffolds, etc. The most common methods to produce such structures involve the use of a solvent with a porogen component, a co-solvent, or a copolymer with sacrificial blocks.1,2 The solvent has to be extracted to obtain the porous material. These methods are ill-suited for closed pore structures, for which it is preferable to use a gas or supercritical fluid which will easily diffuse out of the polymer matrix. Very thin films with closed pores have been produced for electronic or optical applications by Yokoyama et al.3 using templated block copolymer systems. The fugitive medium was CO2, which swells CO2-philic domains at high pressure and leaves voids when the pressure is slowly decreased. A more conventional solid-state batch foaming process was used by Krause4 to nucleate cells in films a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.100 J. Mater. Res., Vol. 28, No. 17, Sep 14, 2013
http://journals.cambridge.org
Downloaded: 04 Apr 2015
made from high Tg polymers, and subsequently expanding these films into partially foamed membranes in a hot oil bath. Miller et al.5,6 used a similar solid-state batch foaming process to make thin films with PEI. The porosity of these membranes remains low (in the range of 20–50%). A major applicati
Data Loading...
