Design,Adhesion And Robustness Of Hierarchically Microstructured Surfaces Prepared By Microinjection Compression Molding

With the rapid development of micro-engineering technology, product miniaturization trend is becoming more and more obvious. The components and products with microstructure play increasingly important role in the fields such as communications, IT, healthcare, automotive and consumer goods. Microinjection compression molding(μ-ICM) combining microinjection molding and nanoimprint lithography is widely used in high-efficient, high-precise, low-cost and large-scale production. In this dissertation, combing theoretical and experimental methods, the high-shear-rate rheological characteristics of three polymer melts are investigated and compared. The effect of processing parameters of μ-ICM on the replication properties of surface microstructure for two materials is investigated. Then large-sized samples with high-aspect-ratio(AR) and intricate microstructure on surfaces are prepared, the formation mechanism, adhesion as well as wetting and mechanical stability of microstructure are analyzed.Capillary rheometers with back pressure regulation are used for measuring the melt shear viscosities of polystyrene(PS), polypropylene(PP), and linear low-density polyethylene(LLDPE) under high shear rates. The rheological characteristics of the three melts are compared through the systematical analyses for three significant effects, namely the end pressure loss, pressure dependence, and dissipative heating in capillary flow. Pronounced end effect begins to appear at the shear rates of 1.6×105, 8.0×105, and 2.8×106 s-1 for the PS, PP, and LLDPE melts, respectively. The significance of the end effect can be ordered as PS ? PP ? LLDPE. The three melts can be ordered as PS ? PP ? LLDPE in terms of total effect, which is the same as the order of their end effect. The end effect exhibits the same order as the pressure coefficient of the shear viscosity, which is related to the molecular structure of polymer. Thus, it seems that the polymers with more complex molecular structures exhibit a higher degree of divergence between the comprehensively corrected and uncorrected melt viscosity curves. Moreover, the dissipation effect begins to predominate over the pressure effect under the lowest shear rate of 105 s-1 for the PS melt among the three melts. The viscosity of the LLDPE melt is highest, and is least sensitive to the shear rate, pressure and temperature.The effect of five processing parameters of μ-ICM, including melt temperature(Tm), injection velocity(VI), mold temperature(TM), mold compression force(FC) and mold compression velocity(VC), on the microstructureed replication properties on the PP and LLDPE samples is investigated. The results show that the TM is the most significant processing parameter that influences the microstructure AR. Effect of the VI and FC on the microstructure AR is more significant for the PP than the LLDPE. The Tm obviously influences the microstructure AR. The microstructure AR is still smaller for the LLDPE than the PP at relatively high TM.The microstructures in the templates are replicated on the surfaces of large-sized PP samples using μ-ICM in one step. The surfaces molded via the two sieves with different meshes exhibit the dual-level microstructure, which consists of micro pyramids with high AR and micro ridges. The surfaces molded via four templates, which consist of the aforementioned two sieves stacked with punched plates with different hole diameters, exhibit three-level microstructure. The three-level microstructure consists of the uniformly distributed micro columns and the aforementioned dual-level microstructures on the top surfaces of the micro columns. All the six surfaces have the static water contact angles(CAs) of above 150? and the rolling angles(RAs) of from 5.5? to more than 90?(i.e., exhibit a wide-ranged manipulation for the adhesion). Overall, superhydrophobic surfaces with diffirent adhesion are obtained through deliberately manipulating the size, shape, and arrangement of microstructures.A flexible template replication method is proposed for the preparation of bio-inspired PP surfaces with microtopographies and gradually tunable water droplet adhesion in one step using ?-ICM. Silica nanoparticles(SNPs) coated on templates are transferred to viscous state-dominated melt during its filling in ?-ICM, and firmly adhered to the skin of the replicas, forming hierarchical microstructures on PP surfaces. The hydrophilic and hydrophobic SNPs on high-AR micropillared surfaces help achieve extremely high(petal effect) and extremely low(lotus effect) adhesion on superhydrophobic surfaces, respectively. Transferring hybrid SNPs to a low-AR micropillared surface turns it from hydrophobic to superhydrophobic and preserves medium adhesion. Gradually tunable and wide-ranged water droplet adhesion on superhydrophobic surfaces is attributed to the geometrical microtopographies of the surfaces in combination with the inherent properties of the SNPs.Applying μ-ICM technology, a fast and flexible method is first proposed for the successive and mass replication of PP samples with T-shaped micropillared surfaces. The water droplet on the titled surfaces grows in size to roll off due to gravitation effect. Interestingly, the RAs on such surfaces are as a quadratic function of specified water droplet volume. This means quantitative droplet collection and lossless transfer can be performed on the replicated surfaces. Meanwhile, self-cleaning behavior is preserved on the surfaces. Moreover, the robust Cassie-Baxter state on the replicated surfaces against the external pressure is demonstrated with droplet compression and sample immersion tests. Specifically, a droplet sitting on the replicated surface can recover its spherical shape after squeezed to a water film as thin as 0.37 mm; and the replica is remained fully spotless after it is submerged into dyed water.Applying μ-ICM, large-sized PP/POE samples with microstructured surfaces are prepared. The POE causes an increase in the CAs on the surfaces to a certain extent. Moreover, the POE not only improves the ductility of surface microstructure, but also increases the friction force between the microstructured surface and sandpaper during the abrasion testing, which is benefit for the formation of secondary structure on the top surface of the micropillars. After 100-cm abrading, the microstructured surface of the PP/POE sample still remains surperhydrophobic, and robust Cassie-Baxter state is demonstrated.