Effect of nanoconfinement on relaxation dynamics & crystallization of molecular glasses Kritika Jha

Format:

Book

Thesis/Dissertation

Author/Creator:

Jha, Kritika, author.

Contributor:

University of Pennsylvania. Chemistry., degree granting institution.

Language:

English

Subjects (All):

Chemistry.

Physical chemistry.

Packaging.

Nanoscience.

0485.

0494.

0565.

0549.

Local Subjects:

Chemistry.

Physical chemistry.

Packaging.

Nanoscience.

0485.

0494.

0565.

0549.

Genre:

Academic theses

Physical Description:

1 online resource (144 pages)

Contained In:

Dissertations Abstracts International 87-12B

Place of Publication:

Ann Arbor : ProQuest Dissertations and Theses, 2026

Language Note:

English

Summary:

Nanoconfinement of molecular glasses within nanoparticle frameworks has been shown to restrict molecular motion and increase glass transition temperature (Tg), driven primarily by reduced configurational entropy and altered relaxation dynamics. This phenomenon is particularly relevant for materials design, enabling enhanced stability and tailored properties. While previous studies have primarily focused on polymeric glasses, this dissertation extends understanding to small-molecule glasses and polymorphic compounds, addressing critical gaps in knowledge regarding nanoconfinement effects on glass transition and relaxation mechanisms.This work first examines the physical aging behavior of molecular glasses, a densification process that reduces free volume and molecular mobility, impairing charge transport and degrading device performance in organic semiconductors. Predicting these time-dependent changes is critical for practical applications. Through collaborative efforts, we studied the physical aging behavior of N, N'-bis(3-methylphenyl)-N, N'-diphenylbenzidine (TPD) glasses using spectroscopic ellipsometry to monitor thickness changes and differential scanning calorimetry (DSC) and flash DSC to examine enthalpy recovery.Building on this molecular system, we investigated kinetic stability by preparing extremely nanoconfined TPD through self-assembled nanoparticle (NP) films via Capillary Rise Infiltration (CaRI). As NP diameter decreases, increasing confinement leads to significant rises in Tg, suggesting the motion of molecules is significantly restricted. We investigated the influence of nanoconfinement on solvent diffusion mechanisms and uptake rates in molecular nanocomposites through in-situ solvent vapor annealing coupled with spectroscopic ellipsometry. The extremely nanoconfined TPD with the smallest nanoparticle size exhibited an uptake rate four orders of magnitude slower in reaching equilibrium chemical potential compared to the pure TPD film, highlighting the significant enhancement in barrier properties achieved through extreme nanoconfinement.Beyond slow kinetics of confined systems, we investigated nanoconfinement strategies applied to acetaminophen, a widely used pharmaceutical exhibiting polymorphism. Confined acetaminophen was produced as a highly stable molecular glass, and we investigated crystallization growth and polymorphic transitions under confinement. Under extreme confinement, the crystallization rate slows by four orders of magnitude. Upon variable temperature cycling that typically induces polymorphic transformations in bulk acetaminophen, the confined system remained intact and resisted polymorphic change even under thermal cycling.Extending these observations in Chapter 5, we studied nanoconfinement effects on polymorphic D-mannitol, a model system with complex phase behavior. Flash DSC was utilized to examine thermal transitions, including Tg, crystallization, and melting behavior under varying nanoparticle sizes. We observed that confinement raises Tg and suppresses crystallization, with noticeable melting point depression compared to bulk.These findings demonstrate that nanoconfinement can modulate molecular mobility, resist polymorphic transitions, and enhance control over crystallization, which is crucial for developing amorphous drug formulations. The improved thermal and kinetic stability can be attributed to reduced molecular dynamics within the nano porous medium. In addition, these nanoconfined materials may function as effective gas barriers for packaging applications, leveraging restricted molecular motion to enhance barrier properties

Notes:

Source: Dissertations Abstracts International, Volume: 87-12, Section: B.

Advisors: Fakhraai, Zahra; Murray, Christopher B. Committee members: Mallouk, Thomas E.; Riggleman, Robert A.

Ph.D. University of Pennsylvania 2026

Vendor supplied data

Local Notes:

School code: 0175

ISBN:

9798247985099

Access Restriction:

Restricted for use by site license