Title: Luminescent tubular precipitation structures from reactant-loaded pellets
Author: Patrick J. Fryfogle Eric J. Nelson Jason J. Pagano
Reference: COLSUA 20141
To appear in: Colloids and Surfaces A: Physicochem. Eng. Aspects
Received date: 3-6-2015
Revised date: 3-9-2015
Accepted date: 4-9-2015
Please cite this article as: Patrick J.Fryfogle, Eric J.Nelson, Jason J.Pagano,
Luminescent tubular precipitation structures from reactant-loaded pellets,
Colloids and Surfaces A: Physicochemical and Engineering Aspects http://dx.doi.org/10.1016/j.colsurfa.2015.09.005
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. 1
Luminescent Tubular Precipitation Structures from Reactant-Loaded Pellets
Patrick J. Fryfogle, Eric J. Nelson, Jason J. Pagano* firstname.lastname@example.org
Department of Chemistry, Saginaw Valley State University, University Center, MI 48710-0001 (USA) *Corresponding author. Tel: 01 989 964 2638; Fax: 01 989 964 2796. 2
Graphical Abstract 3
Highlights -Pellets containing ZnSO4 and ZnS form tubes when sodium silicate is poured on them. -Tube growth is directed by a gas bubble attached to the surface of the colloidal membrane. -The growth kinetics and morphology of tubular precipitates are monitored by a timelapse camera. -Scanning electron microscopy (SEM) is used to characterize the precipitation patterns. -The tubes exhibit photoluminescence upon excitation. 4
Using reaction conditions far from equilibrium, we are able to produce hollow tubes formed from reactant-loaded pellets. The latter pellets are composed of zinc sulfate and phosphorescent zinc sulfide by mass. During the experiment, a single pellet is fixed at the bottom of a container and then a small volume of concentrated sodium silicate is poured on the pellet’s surface. Dilatory tube growth is directed by a single gas bubble which is monitored by a time-lapse camera. Using procedures of image acquisition and processing we are able to quantify the spatio-temporal dynamics. Systematic measurements include induction period and growth velocity. We describe two distinct morphologies of precipitation tubes which form at the interface of the two reactants. The resulting tubes can range from 1.1-1.8 mm and 450-900 µm in radii depending on the morphology. Scanning electron microscopy reveals that the precipitation tubes have intricate patterns on the outside surface. Lastly, the tubes exhibit photoluminescence upon exposure to ultraviolet light.
Keywords: inorganic surface science; interfacial processes; soft matter; chemobrionics; self-organization; luminescence. 5 1.0 Introduction
Self-organization in aqueous reaction-precipitation systems often leads to the formation of permanent architectures. The two most prominent inorganic precipitation systems of laboratory study are silica biomorphs and chemical gardens or silica gardens . Silica biomorphs are obtained from the precipitation of barium or strontium carbonates in silica-rich alkaline environments which yield crystalline aggregates that resemble the morphology of primitive organisms [2,3]. In the conventional chemical garden experiment, plant-like tubular structures are formed when water soluble metal salt crystals (e.g., CaCl2, CuSO4, FeCl3) make contact with solutions of silicate or other anions . In the context of chemical gardens, tube formation is based on a semipermeable membrane around the dissolving seed crystal . The difference in the osmotic pressure on the two sides of the membrane allows for the inflow of water from the outside alkaline silicate causing the expansion and rupture of the inner acidic membrane. The continuous dissolution of the acidic seed crystal results in a far-fromequilibrium state via a continuous osmotic pumping action into the ambient basic silicate solution. The precipitation of amorphous silica with metal hydroxides (or oxides) give rise to tubular structures which grow upwards with speeds of mm/day or mm/s.
Chemical gardens have been explored since the 17th century . Many of these early explorations were motivated by the colorful “life-like vegetation” observed during the reaction. In the early 20th century, researchers considered these structures to be pre-biotic and models for the origin of life because they exhibit similarity to biological structures [7,8]. Clearly, advances in biochemistry, in particular, the discovery of DNA 6 during the middle of the 20th century dismissed these notions. Nevertheless, chemical gardens are familiar to scientists and non-scientists alike because they are widely used today as a demonstration experiment in chemical education.
In recent years, many different experimental techniques geared toward the synthesis and control of hollow tubular precipitation structures have been reported in the literature. Most of the literature discusses single day formation or rapid growth of tubes from reactants including seed crystals [9,10], pressed pellets of pure compounds  and reagent-loaded polymer beads . All of the latter reactants are capable of being replaced by a seed solution of which is hydrodynamically delivered to the other reactant through a glass nozzle at predetermined flow rates [16-19]. In addition, the solution delivery or flow technique can be modified by templating a gas bubble to the forming tube thus creating highly linear structures [20,21]. The tubes generated by buoyant gas bubbles show many interesting materials features. For instance, the preparation of photocatalytically, photoluminescent silica/ZnO  and superparamagnetic silica/magnetite tubes . Recently, Roszol et al. demonstrated the postsynthetic processing of bubble-guided silica/Cu(OH)2 tubes by physical and chemical means . Another key advancement is the work done by Steinbock and coworkers who reported the incorporation of CdSe-ZnS quantum dots into macroscopic silica/ZnO tubes .