3 research outputs found
Role of the Branched PEG‑<i>b</i>‑PLLA Block Chain in Stereocomplex Crystallization and Crystallization Kinetics for PDLA/MPEG‑<i>b</i>‑PLLA‑<i>g</i>‑glucose Blends with Different Architectures
The
isothermal crystallization behavior and corresponding morphology
evolution of poly(d-lactic acid) (PDLA) blends with PLLA6.7k or MPEG-b-PLLA6.7k-g-glucose with different architectures and different PLLA-grafted
copolymer contents were investigated. The formation of stereocomplexes
(SCs) in between the chain branched structure of MPEG-b-PLLA6.7k-g-glucose and PDLA chains acting
as the physical crosslinking points slows down the motion of PDLA
chains, but the SCs could act as a heterogeneous nucleating agent
for the late formation of homocrystals (HCs) in the blend system,
accelerating the crystallization kinetics of HCs through enhancing
the nucleation density. For PDLA/MPEG-b-PLLA6.7k-g-glucose blends, the mobility of SCs
in the blend system and the nucleation density of SCs in the blends
exhibit oppositional behavior during the isothermal crystallization
at a Tc of 130 °C. The evolution
of the crystal growth and structure during the isothermal crystallization
process by rheometry has revealed the interesting role of the branched
chains of MPEG-b-PLLA6.7k-g-glucose in the mechanism of the crystallization in PDLA blends
Design of Heterogeneous Nuclei Composed of Uniaxial Cellulose Nanocrystal Assemblies for Epitaxial Growth of Poly(ε-caprolactone)
Epitaxial crystallization
is the most prominent approach to achieving
oriented thin films composed of semicrystalline polymers (SCPs). Nevertheless,
current templates remain limited in fulfilling oriented SCPs with
high-throughput coating processes. Herein, we report the first template
for the epitaxial crystallization of SCPs based on a uniaxial assembly
of shape-anisotropic nanocrystalsî—¸cellulose nanocrystals (CNCs).
The template was fabricated via a dip-coating method, leading to a
uniaxial thin coating on both planar and nonplanar substrates. Such
a thin coating functioned similarly to a laterally oriented SCP thin
film in regulating the crystallization behaviors of polyÂ(ε-caprolactone)
(PCL). The orientational relationship between the CNC thin coating
and the PCL overlayer was studied systematically by employing multiple
characterization tools including scattering, diffraction, and microscopy.
Moreover, the epitaxial match based on the crystallography-regulated
hydrogen-bonding networks between the two layers was confirmed by
molecular modeling, in agreement with the experimental results. Besides
the orientational regulation, CNCs also promoted the crystallization
kinetics of PCL effectively due to the nanoepitaxial effect provided
by each CNC particle. We highlight this facile assembly approach to
heterogeneous nuclei for the epitaxial crystallization of SCPs and
its extendability of achieving thin coatings composed of 3D-oriented
SCPs on ambient substrates
Design of Heterogeneous Nuclei for Lateral Crystallization via Uniaxial Assembly of Cellulose Nanocrystals
Semicrystalline
polymers (SCPs) represent a group of cheap heterogeneous nuclei for
crystallization. Nevertheless, cellulose, the most abundant biogenic
SCP, is notorious for its poor processability. This limits its application
as the orientational guiding agent in crystallization of functional
compounds. Different from current polymer engineering approaches to
uniaxial SCP thin films, we explored a novel approach to the uniaxial
cellulose thin film via the oriented assembly of cellulose nanocrystals
(CNCs) by means of a simple dip-coating technique. This thin film
successfully guides the lateral crystallization of two drug compounds,
which in turn reflects the uniformity of the uniaxial CNC alignment
on the macroscopic scale. Furthermore, unlike traditional SCP thin
films, the assembly route driven by different external forces can
lead to CNC thin films with distinct orientational characters for
fabrication of patterned drug thin films. The emerging colloidal assembly
route to a uniaxial SCP substrate leads to unprecedented access to
design heterogeneous nuclei for oriented crystallization of functional
hybrids