Digital holography as metrology tool at micronanoscale for soft matter

The appearance of the first laser approximately 12 years after the invention of holography by Gabor(1948)revolutionized the field of optical metrology.In fact,the invention of holographic interferometry enabled the exploitation of interferometry on non-mirror surfaces and full-scale objects.The holography-based measurement methods has been implemented to several industrial systems or in support of R&D with the aim of improving new products in many fields(automotive,aerospace,electronics,etc.).To date,holography has been considered an important measurement tool for non-destructive inspection(NDI),strain-stress measurement,and vibration analysis at various engineering sites.Recently,the new paradigm of Industry4.0 has seen the introduction of new technologies and methods of processing materials as well as the development of manufacturing approaches for the realization of innovative products.For example,direct printing,additive,and bottom-up manufacturing processes are expected to involve new ways of making products in future,and most innovative fabrication processes will be based on the manipulation of soft matter(e.g.,starting from the liquid phase)that will be shaped at the nanoscale.The inherent characteristics of digital holography(DH)make it a powerful and accurate tool for the visualization and testing of final products,as well as for in situ and real-time monitoring and quantitative characterization of the processes involved during the fabrication cycle.This review aims to report on the most useful applications of soft matter,where the capabilities offered by DH,such as three-dimensional(3D)imaging,extended focus,3D tracking,full-field analysis,high sensitivity,and a wide range of measurements from nanometers to centimeters,permit completely non-invasive characterizations on a full-scale.Several holographic experimental results of typical samples are reported and discussed where DH plays a primary role as a tool gauge for soft matter.

Quantitative imaging of the complexity in liquid bubbles’evolution reveals the dynamics of film retraction

The dynamics and stability of thin liquid films have fascinated scientists over many decades.Thin film flows are central to numerous areas of engineering,geophysics,and biophysics and occur over a wide range of lengths,velocities,and liquid property scales.In spite of many significant developments in this area,we still lack appropriate quantitative experimental tools with the spatial and temporal resolution necessary for a comprehensive study of film evolution.We propose tackling this problem with a holographic technique that combines quantitative phase imaging with a custom setup designed to form and manipulate bubbles.The results,gathered on a model aqueous polymeric solution,provide unparalleled insight into bubble dynamics through the combination of a full-field thickness estimation,threedimensional imaging,and a fast acquisition time.The unprecedented level of detail offered by the proposed methodology will promote a deeper understanding of the underlying physics of thin film dynamics.

Hollow micro- and nano-particles by gas foaming

This paper presents the results of a first successful attempt to produce hollow micro- and nano-particles of a large variety of materials, dimensions, shapes and hollow attributes by using an environmentally friendly and cheap technology, common in polymer processing and known as gas foaming. The central role played by ad hoc polymeric hollow micro- and nano-particles in a variety of emerging applications such as drug delivery, medical imaging, advanced materials, as well as in fundamental studies in nanotechnology highlights the wide relevance of the proposed method. Our key contribution to overcome the physical lower bound in the micro- and nano-scale gas foaming was to embed, prior to foaming, bulk micro- and nano-particles in a removable and deformable barrier film, whose role is to prevent the loss of the blowing agent, which is otherwise too fast to allow bubble formation. Furthermore, the barrier film allows for non-isotropic deformation of the particle and/or of the hollow, affording non-spherical hollow particles. In comparison with available methods to produce hollow micro- and nano-particles, our method is versatile since it offers independent control over the dimensions, material and shape of the particles, and the number, shape and open/closed features of the hollows. We have gas- foamed polystyrene and poly-（lactic-co-glycolic） acid particles 200 ~m to 200 nm in size, spherical, ellipsoidal and discoidal in shape, obtaining open or closed, single or multiple, variable in size hollows.