聚對苯二甲酸辛二酯[poly(octamethylene terephthalate), POT]及聚對苯二甲酸壬二酯[poly(nonamethylene terephthalate), PNT]的薄膜結晶或三度空間的結晶以偏光顯微鏡、微分掃描卡度計、掃描式電子顯微鏡及穿透式電子顯微鏡作觀察和分析。POT可以同時呈現兩種結晶型態，分別是有雙層環帶(double ring-banded)的球晶和沒有環帶(ringless)的球晶，其分佈依結晶溫度(Tc)或熔融溫度(Tmax)而不同。當使用160oC為熔融溫度的情況下，兩種結晶的比例會隨結晶溫度改變：在較低的結晶溫度，POT沒有環帶的球晶比例比較多；而在較高的結晶溫度下，POT則呈現全部是環狀光環的球晶。而在同一且較低的結晶溫度下，熔融溫度的提高會使沒有環帶球晶的比例減少，顯示高的熔融溫度可以把沒有環帶球晶的晶核全部熔掉。
PNT則有三種結晶，分別稱為類型0、類型1及類型2球晶；其中只有兩種球晶會出現在同一結晶溫度。在較低結晶溫度(低於55oC)下，沒有環帶球晶的類型0，和雙層環帶球晶的類型2共存。而當結晶溫度高於55oC，佔多數的單層環帶(single ring-banded)類型1球晶和佔少數的類型2球晶共存。在掃描式電子顯微鏡的觀察下，相較於類型1球晶，類型2球晶環帶間距明顯較寬，其排列比較像是許多的短棒圍成的環狀同心圓結構，且其環狀結構也較類型1整齊。
除了薄膜結晶的分析外，PNT三度空間的結晶也首次在本研究中探討。環狀結構不只在塊狀結晶的表面中被發現，其內部剖面也有類似的結構。經由掃描式電子顯微鏡和穿透式電子顯微鏡的分析，塊狀結晶內部的切片呈現在薄膜狀態的環狀結構相似。在塊狀結晶中，PNT類型1球晶和在薄膜的情況一樣佔多數，而類型2球晶則佔少數。在選定的幾個結晶溫度下做塊狀結晶的內部分析，推測PNT結晶在立體狀態下，是層狀成長而變成多層次的環狀立體結構。
通常PNT類型2球晶很難被發現，該數量非常稀少。然而若將塊狀PNT在壓錠後的溴化鉀片上結晶，則可以得到類型2球晶佔整塊結晶幾乎是一半的比例，該結晶會出現在與溴化鉀片的接觸面(底面)，而在整個塊狀結晶的表面(接觸空氣的那面)則清一色為類型1球晶。由表面或底面連接內部剖面的圖來看，PNT環狀結構的結晶應為非結晶層與結晶層交替形成。從薄膜到三度空間的結果，PNT的環狀結構形成機制可略知ㄧ二。

Spherulite morphology of poly(octamethylene terephthalate) (POT) and poly(nonamethylene terephthalate) (PNT) in thin-film or three dimensional forms, were characterized using polarized versus non-polarized optical microscopy, scanning electron microscopy (SEM), wide-angle X-ray (WAXD) analysis, and transmission electron microscopy (TEM). POT can simultaneously display solely one type of spherulite or dual types of spherulites (double-ring-banded and ringless ones), depending on Tc or Tmax imposed. Fractions of these two types depend on Tc when quenched from a fixed Tmax = 160oC. At lower Tc’s, POT exhibits higher crystallization rates leading to higher fractions of ringless spherulites; at higher Tc’s, POT exhibits lower crystallization rates leading to ring-banded spherulites.
Three types of spherulites (labeled: Type-0, 1, and 2) are possible in PNT when crystallized at wide range of crystallization temperature (Tc); however, only two of the three types can coexist in PNT at a given Tc. At lower Tc (lower than 55oC), the spherulites in PNT are either of Type-0 (appearing ringless in POM) or Type-2 (double-band in POM). When crystallized at 55oC or higher, the morphology is featured with Type-1 (single-ring-banded in POM) spherulites as the majority species that co-exist with Type-2 spherulites as imbedded minority. By comparison, the rod-like lamellae in the double-banded spherulites (Type-2) are longer and thicker, and more ordered than those in the single-banded spherulites (Type-1).
Morphology of crystallized spherulites in PNT in bulk forms, instead of thin-film forms, was investigated. Ring textures were found to exist on the fractured surfaces or microtomed films from bulk PNT samples. By further SEM and TEM examinations, the fracture surfaces and microtomed films from the interior of the bulk display similar ring-banded patterns as those in thin films cast on glass slides. Although the cast PNT thin films in two-dimensional growth are known to display both Type-1 ring bands as majority and Type-2 ring bands as minority, this study further shows that the interior of PNT bulk exhibits mainly Type-1 (single rings with narrower spacing than Type-2) ring bands, and Type-2 spherulites exist sporadically in three-dimensional forms. From these analyses on the ring bands in the interiors of bulk-form PNT crystallized at several specific temperatures, it can be proposed that the growth of spherulites in three dimensions is layer-by-layer, packing into a multi-shells structure in three-dimensional ring-banded spheres. The rarely seen Type-2 spherulites are observed to be increased in population when crystallized on KBr substrates. From the relationship of the top or bottom surface and the fractured surface of bulk PNT taken off from KBr substrate it shows that the ring-band patterns exhibited on the top or bottom surface are actually the multi-shell construction with crystalline and non-crystalline layers alternating in spherulite of the bulk.

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