Mold filling involves flow of polymer melts and solidification of the melt starting at the walls. Fountain flow describes how the polymer fills the mold cavity. Molecules from the center of the cavity flow towards the wall and form a stable skin layer. This causes a higher degree of molecular orientation in the skin layer compared to bulk.
Optical and SEM micrographs of injection-molded PP μC (mold temperature 80 °C). The scale bars correspond to 100 μm. The images of the first and second rows demonstrate the development from the first- to the second-generation injection molds. The optical micrographs show rim-like regions at the edges of the μC.
Wide-angle x-ray scattering patterns of the first generation μC measured at the rim (top row) and center (bottom row). The WAXS patterns from rim and center only differ in intensity.
SAXS intensity distribution (286–418 nm) integrated along the first generation μC. High scattering intensities are present at the rim-like regions for COC, PP, POM, and PEEK. The constant full-width-at-half-maximum of (21.8 ± 0.5) μm is attributed to edge scattering and characterizes the x-ray beam width. The edge scattering even shows a preferential orientation as indicated by the inset. The orientation is color-coded according to the color wheel inset. The gray area indicates the width of the cantilever, while the gradient of the gray color indicates the thickness.
The SAXS pattern at the center of PVDF, POM, and PP second-generation μC exhibit characteristic features, which become closer for higher mold temperatures. This means the observed nanostructures increase with the mold temperature.
The spots of the SAXS pattern shown in Fig. 5 are quantified using the peak intensity I peak, the q-value at the peak q peak, and the full-width-at-half-maximum FWHMpeak of the spot derived from a fit to a Lorentzian (cf. Table I). The graph shows this procedure exemplarily for POM using the mold temperature of 150 °C.
The spatially resolved SAXS pattern (16 points across the width of the second-generation μC) demonstrates the homogeneity of the POM, PVDF, and PP μC using the three fitted parameters (cf. Fig. 6).
The azimuthal plot (q-range of 0.35–0.51 nm− 1) of the mean scattered intensity of second-generation POM μC injection molded with a mold temperature 150 °C elucidates the orientation of the related nanostructures. The degree of orientation is determined by means of I max and I min.
Nanostructure characterization of micro-cantilevers injection-molded at different mold temperatures. Mean values and related standard deviations of the three Lorentzian fitted values and the degree of anisotropy of the central region of the cantilever.
Nanostructure characterization of micro-cantilevers injection-molded with different injection speeds. Mean values and related standard deviations of the three Lorentzian fitted values and the degree of anisotropy of the central region of the cantilever.
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