Patterned-charge Marked Relaxation Of Thin Polymers Studied By Atom Force Microscopy

Polymer films have significant applications, including protective and lubricating coatings, adhesives, high performance composite materials, microelectronic encapsulants and dielectrics. The emergence and rapid development of nano science and technology have raised the demand that the thickness of the film should be deducted into nanometer range. However, it is widely known that owing to the small size confinement effect especially when it comes to nano scale, the properties of thin polymer films, including those related to crystallization, physical cross-linking in polymers, thermal expansion coefficients, physical aging and glass transition temperature (Tg) et.al, display great differences compared with that of bulk materials. which are all essentially caused by the polymer film relaxation. Thus, it’s of great scientific significance to study the relaxation properties of polymer thin and ultrathin film so that it can be better used.In this paper, we have constructed patterned charge on the polymer films and the patterned charge also acts as a mark. With the help of Atom Force Microscopy (AFM), we have conducted a real time monitoring of the patterned charge decay rules during the polymer relaxation process and studied the dielectric relaxation properties of the polymer films and the relationship between the Tg and dielectric relaxation. What’s more, some key influence factors are discussed. This method has the advantages of intuition and accuracy. The main conclusions of this paper are as follows:1. With the method of micro-contact printing(μ-CP), we can quickly construct patterned charge on the electret polymer films, which will not change the surface morphology and properties of the films;2. When functioned with a constant temperature, the surface potential of polymer films shows an exponential decay, namely a sharp decay in the beginning several minutes and a gentle decreasing followed with time lasting. Moreover, The film with an initial higher potential shows a more faster decay and when the decay tends to be stable, the remanent potential is much higher.3. The patterned charge decay tendency of polymer films with temperature increasing shows two spinodals and the temperature corresponding to the two spinodals comes at low and high temperature can be respectively defined as the film surface Tg (Tgs) and the Tg of whole film, which gives a new way of polymer Tg measurement. According to this, the experiment result reveals that the Tg of polymer film reduced with film thickness decreasing, which agrees well with the widely reported relation between Tg and film thickness.4. The surface potential decay of ultrathin film with temperature increasing is studied and the result shows that the decay process of 10nm ultrathin film displays a linear decay and a spinodal can be obviously seen when the decay rate is changed. The temperature related to this spinodal can also be defined as the Tg of the film. Using the pattern charge to study the relaxation of ultrathin film can overcome the error existing in the traditional study since the film is too thin. Detecting the charge decay rules with EFM of high sensitivity, has the function of magnifying the relaxation signals, which provides a feasible way to study the relaxation and it’s dynamics process of polymer film and especially ultrathin film.